Snippet Name: Postgres_vs_SQL_Server_Schemas
Tags:
Created Date: 2025-06-16 13:12:38
Last Modified Date: 2025-05-31 10:32:00
Dependencies:
DBA Notes:
Sample Output:
Title: Postgres vs SQL Server Schemas
Author: user
I come from a SQL Server background, where a database named "SandBox" can have more than one schema, and each schema can have multiple tables. Can you compare PostGres database systems for me? It seems to me that postgres expects all user tables in a "SandBox" database to be placed in a the public schema
Author: ChatGPT
Your observation is partly correct, but PostgreSQL's design is very similar to SQL Server in terms of supporting multiple schemas within a single database. Let me compare and explain the key differences and similarities between SQL Server and PostgreSQL schemas and database organization:
---
### **SQL Server:**
1. **Databases and Schemas:**
- A SQL Server instance can host multiple databases.
- Within each database, you can create multiple schemas.
- Each schema acts as a namespace for objects (tables, views, stored procedures, etc.).
- Default schema for most users is `dbo`, unless explicitly changed.
2. **Access and Ownership:**
- Schemas can have specific owners.
- Permissions can be applied at the schema level or object level.
3. **Object References:**
- Fully qualified naming convention: `[DatabaseName].[SchemaName].[ObjectName]`.
- Example: `SandBox.dbo.MyTable`.
---
### **PostgreSQL:**
1. **Databases and Schemas:**
- PostgreSQL also supports multiple databases within an instance.
- Each database can have multiple schemas.
- Default schema is `public`, but you are not limited to it. You can create and use as many schemas as you like.
2. **Search Path:**
- PostgreSQL uses a `search_path` to determine which schema is checked first when accessing an object.
- By default, `search_path` includes `"$user", public`, meaning it looks for objects in the schema matching the current user name and then in the `public` schema.
3. **Object References:**
- Fully qualified naming convention: `database.schema.object`.
- Example: `SandBox.public.my_table`.
4. **Differences in Usage:**
- Many users stick to the `public` schema for simplicity.
- Schemas are often used to organize objects for different modules or applications in the same database.
- Unlike SQL Server, there's no concept of a `dbo` schema. The `public` schema is a convention, not a requirement.
---
### **Key Points of Comparison:**
| Feature | SQL Server | PostgreSQL |
|-------------------------|------------------------------------------|----------------------------------------|
| Default Schema | `dbo` | `public` |
| Multiple Schemas | Supported | Supported |
| Schema Ownership | Each schema has an owner | Each schema has an owner |
| Object Reference | `[Database].[Schema].[Object]` | `database.schema.object` |
| Search Path | Implicitly checks `dbo` for most users | Uses `search_path` for schema priority |
| Schema Use Best Practice| Organize objects by module/application | Organize objects by module/application |
---
### **Customizing Schema Use in PostgreSQL:**
If you don???t want to put all user tables in the `public` schema:
1. **Create a New Schema:**
```sql
CREATE SCHEMA sandbox_schema;
```
2. **Change the Default Schema:**
Update the `search_path` to prioritize the new schema:
```sql
SET search_path TO sandbox_schema, public;
```
3. **Use Fully Qualified Names:**
When creating or referencing tables:
```sql
CREATE TABLE sandbox_schema.my_table (id SERIAL PRIMARY KEY, name TEXT);
SELECT * FROM sandbox_schema.my_table;
```
---
### **Conclusion:**
PostgreSQL is flexible and supports multiple schemas just like SQL Server. While many PostgreSQL users place tables in the `public` schema by default, this is a convention rather than a limitation. You can create and use as many schemas as needed within a database, just as you would in SQL Server, and you can manage access, organization, and naming in a similar fashion.
Author: user
does postgres support cross dataabase queries then? assuming the user has access to both schemas?
Author: ChatGPT
PostgreSQL **does not natively support cross-database queries** within a single instance in the way SQL Server does. In SQL Server, you can query across databases on the same instance using fully qualified names (e.g., `DatabaseName.SchemaName.ObjectName`). However, PostgreSQL limits queries to a single database per connection.
That said, there are workarounds and tools available to achieve similar functionality. Here???s a breakdown of the options:
---
### **1. Cross-Database Queries within PostgreSQL:**
#### **Why Not Natively?**
- PostgreSQL databases are designed to be isolated from one another.
- Each database has its own schema namespace, catalog, and set of connections.
#### **Workarounds for Cross-Database Access:**
##### **a. Use `dblink` Extension**
- **Overview**: `dblink` allows connections to other databases and executes queries in those databases.
- **Setup**: You need to install the `dblink` extension.
- **Example**:
```sql
CREATE EXTENSION dblink;
SELECT *
FROM dblink('dbname=otherdb user=youruser password=yourpassword',
'SELECT id, name FROM schema_name.table_name')
AS t(id INT, name TEXT);
```
- **Use Case**: Quick and simple access to another database.
##### **b. Use `postgres_fdw` (Foreign Data Wrapper)**
- **Overview**: `postgres_fdw` allows you to define foreign tables that point to tables in other PostgreSQL databases, enabling queries across them as if they were local tables.
- **Setup**:
1. Create the extension:
```sql
CREATE EXTENSION postgres_fdw;
```
2. Create a foreign server and user mapping:
```sql
CREATE SERVER otherdb_server
FOREIGN DATA WRAPPER postgres_fdw
OPTIONS (host 'localhost', dbname 'otherdb', port '5432');
CREATE USER MAPPING FOR current_user
SERVER otherdb_server
OPTIONS (user 'other_user', password 'other_password');
```
3. Import schema or create foreign tables:
```sql
IMPORT FOREIGN SCHEMA public
FROM SERVER otherdb_server
INTO local_schema;
```
4. Query the foreign table:
```sql
SELECT * FROM local_schema.foreign_table;
```
- **Use Case**: Seamless integration for frequent or complex cross-database queries.
---
### **2. Alternatives to Cross-Database Queries**
##### **a. Consolidate Data into a Single Database with Multiple Schemas**
- PostgreSQL supports multiple schemas within a database. Instead of splitting data across multiple databases, organize it into schemas:
```sql
CREATE SCHEMA schema1;
CREATE SCHEMA schema2;
CREATE TABLE schema1.table1 (id SERIAL PRIMARY KEY, name TEXT);
CREATE TABLE schema2.table2 (id SERIAL PRIMARY KEY, value TEXT);
SELECT *
FROM schema1.table1 t1
JOIN schema2.table2 t2 ON t1.id = t2.id;
```
##### **b. Use ETL or Replication Tools**
- Tools like `pg_dump`, `pg_restore`, or third-party ETL tools can replicate data from one database to another for centralized querying.
##### **c. Query Across Databases with Middleware**
- Applications or middleware (e.g., Python, Java, or Node.js) can connect to multiple databases and perform joins or transformations in the application layer.
---
### **Comparison of Workarounds**
| Feature | `dblink` | `postgres_fdw` | Single Database with Schemas |
|---------------------------|-------------------------------|-------------------------------------|------------------------------|
| Ease of Use | Simple for ad-hoc queries | Better for frequent integration | Simplifies data organization |
| Performance | Slower for large data | More efficient | Best performance |
| Setup Complexity | Minimal | Moderate | Minimal |
| Schema Independence | Separate databases remain | Separate databases remain | Unified schemas |
---
### **Conclusion:**
PostgreSQL does not natively support cross-database queries. However, extensions like `dblink` or `postgres_fdw` can bridge the gap effectively, allowing you to query across databases. For better performance and simplicity, consider consolidating data into a single database using schemas if that aligns with your design needs.
Author: user
how does PostGres handle temporary tables?
Author: ChatGPT
PostgreSQL handles temporary tables similarly to SQL Server but with some notable differences in behavior and usage. Here's a detailed comparison of how PostgreSQL manages temporary tables:
---
### **1. Key Characteristics of Temporary Tables in PostgreSQL**
- **Scope**: Temporary tables exist only for the duration of a session or a transaction, depending on how they are defined.
- **Namespace**: Temporary tables are created in a special schema visible only to the current session. This ensures no naming conflicts with permanent tables.
- **Isolation**: Each session sees only its own temporary tables, even if multiple sessions create tables with the same name.
---
### **2. Syntax for Creating Temporary Tables**
- **Basic Syntax**:
```sql
CREATE TEMP TABLE temp_table_name (
column_name1 datatype,
column_name2 datatype
);
```
- **Keyword Variations**:
- `TEMP` and `TEMPORARY` are interchangeable.
- Example:
```sql
CREATE TEMPORARY TABLE temp_data (
id SERIAL PRIMARY KEY,
name TEXT
);
```
- **Example with Transactional Scope**:
```sql
BEGIN;
CREATE TEMP TABLE temp_data (
id SERIAL PRIMARY KEY,
name TEXT
);
-- Temporary table is visible here.
COMMIT;
-- Temporary table is dropped automatically.
```
---
### **3. Behavior of Temporary Tables**
1. **Lifetime:**
- Temporary tables are dropped automatically when the session ends.
- If created within a transaction, they are dropped at the end of the transaction if the transaction is rolled back or committed.
2. **Schema Placement:**
- Temporary tables are placed in a special temporary schema that is first in the `search_path` for the session.
3. **Visibility:**
- Only the session that creates the temporary table can access it.
- Other sessions cannot see or interfere with the temporary table.
---
### **4. Differences from SQL Server Temporary Tables**
| Feature | PostgreSQL Temporary Tables | SQL Server Temporary Tables |
|-----------------------------|-----------------------------------------------|-------------------------------------------|
| **Naming** | No special prefix required | Uses `#` for local and `##` for global |
| **Scope** | Session or transaction | Local: Session; Global: Across sessions |
| **Visibility** | Only visible to the creating session | Local: Only in creating session; Global: All sessions |
| **Schema** | Exists in a special temporary schema | Stored in `tempdb` system database |
| **Lifetime** | Session or transaction end | Local: Session end; Global: Explicit drop |
| **Creation Requirements** | No explicit schema requirement | Stored in `tempdb` |
---
### **5. Advantages of PostgreSQL Temporary Tables**
1. **Automatic Cleanup**:
- They are dropped automatically at the end of the session or transaction, reducing the need for explicit cleanup.
2. **No Naming Conflicts**:
- Temporary tables are isolated in their session-specific schema, so there are no naming conflicts with permanent tables or other sessions.
3. **Custom Indexes and Constraints**:
- You can create indexes, primary keys, and unique constraints on temporary tables just like regular tables:
```sql
CREATE TEMP TABLE temp_data (
id SERIAL PRIMARY KEY,
name TEXT UNIQUE
);
```
4. **Efficient for Complex Queries**:
- Temporary tables are efficient for breaking down complex queries into smaller, manageable steps within a session.
---
### **6. Common Use Cases**
- **Staging Data**:
Temporary tables are ideal for staging intermediate results before inserting them into permanent tables.
```sql
CREATE TEMP TABLE temp_stage AS
SELECT * FROM source_table WHERE condition;
```
- **Debugging and Development**:
Temporary tables can be used during query development to test intermediate results.
- **Transactional Scope**:
Temporary tables within a transaction ensure the intermediate data is cleaned up when the transaction ends.
---
### **7. Example Workflow**
```sql
-- Start a session or transaction
BEGIN;
-- Create a temporary table
CREATE TEMP TABLE temp_orders (
order_id SERIAL PRIMARY KEY,
customer_name TEXT,
total_amount NUMERIC
);
-- Insert data into the temporary table
INSERT INTO temp_orders (customer_name, total_amount)
VALUES
('Alice', 100.50),
('Bob', 200.00);
-- Query the temporary table
SELECT * FROM temp_orders;
-- Commit transaction (if needed)
COMMIT;
-- Temporary table is dropped automatically when session ends
```
---
### **8. Notes and Limitations**
- **Indexes and Constraints**:
- You can add indexes and constraints to temporary tables just like permanent tables, but they are valid only for the lifetime of the table.
- **Disk Storage**:
- Temporary tables may be written to disk if their size exceeds the available memory.
- **Performance**:
- Temporary tables can benefit from PostgreSQL's optimizations for in-memory operations if they remain small.
---
### **Conclusion**
PostgreSQL handles temporary tables in a robust and efficient manner, providing features similar to SQL Server but with better isolation and automatic cleanup. Temporary tables are scoped to a session or transaction and reside in a special schema, ensuring no conflicts with permanent tables. They are a powerful tool for intermediate data manipulation, debugging, and transaction-scoped operations.
Author: user
comments appear to be like mysql, which is two dashes and a space, correct?
Author: ChatGPT
Yes, PostgreSQL comments are indeed similar to MySQL in that they can use double dashes (`--`) for single-line comments, but with the requirement of a **space after the dashes**. Here???s a breakdown of comment styles in PostgreSQL:
---
### **1. Single-Line Comments**
- Use `--` followed by a space for a comment. Everything after `--` on the same line is ignored by the database.
- **Example**:
```sql
-- This is a single-line comment
SELECT * FROM my_table; -- This comment is inline
```
---
### **2. Multi-Line Comments**
- Use `/* */` for multi-line or block comments, similar to C-style comments.
- These comments can span multiple lines and do not require a space after `/*`.
- **Example**:
```sql
/*
This is a multi-line comment.
It can span multiple lines.
*/
SELECT * FROM my_table;
```
---
### **Comparison to MySQL Comments**
| Type | PostgreSQL | MySQL |
|--------------------|--------------------------------------|-------------------------------------|
| Single-line | `-- comment` (space required) | `-- comment` (space required) |
| Multi-line | `/* comment */` | `/* comment */` |
| Alternative Single | Not supported | `# comment` |
---
### **Key Notes for PostgreSQL Comments**
1. **Space Required After `--`**:
- Without a space, `--` is not recognized as a comment in PostgreSQL.
- **Invalid Example**:
```sql
--This is not a valid comment in PostgreSQL.
```
**Valid Example**:
```sql
-- This is a valid comment in PostgreSQL.
```
2. **Inline Comments**:
- Inline comments are supported after a statement or clause.
- **Example**:
```sql
SELECT * FROM my_table; -- Fetch all rows
```
3. **Block Comments Nesting**:
- PostgreSQL supports nested block comments, unlike some other databases.
- **Example**:
```sql
/*
This is a block comment.
/* Nested block comment */
*/
SELECT 1;
```
---
### **Conclusion**
PostgreSQL comments behave much like MySQL???s, particularly for single-line comments (`--`) and multi-line comments (`/* */`). However, PostgreSQL does not support the hash (`#`) syntax for comments, which MySQL does. Always ensure there's a space after `--` for single-line comments to be valid in PostgreSQL.
Author: user
how does postgres handle default constraints? can i have named constraints like SLq Server does like "BillingDate" TIMESTAMP(3) NOT NULL CONSTRAINT "DF_Account_BillingDate" DEFAULT (getdate()),
Author: ChatGPT
Yes, PostgreSQL supports named constraints, including **default constraints**, though its syntax differs slightly from SQL Server. PostgreSQL handles `DEFAULT` values at the column level and allows you to explicitly name constraints for better management and readability.
Here???s how it works:
---
### **1. Defining Default Constraints in PostgreSQL**
PostgreSQL allows `DEFAULT` values for columns, but **default constraints are not named automatically** like in SQL Server. You can name a `DEFAULT` constraint explicitly by using the `CONSTRAINT` keyword.
#### **Example with Named Constraint:**
```sql
CREATE TABLE accounts (
account_id SERIAL PRIMARY KEY,
billing_date TIMESTAMP(3) NOT NULL
CONSTRAINT DF_Account_BillingDate DEFAULT CURRENT_TIMESTAMP
);
```
- **Explanation**:
- `CONSTRAINT DF_Account_BillingDate` names the default constraint explicitly.
- `DEFAULT CURRENT_TIMESTAMP` sets the default value for the `billing_date` column.
---
### **2. Equivalent to SQL Server's `getdate()`**
- In PostgreSQL, the equivalent of `GETDATE()` is `CURRENT_TIMESTAMP`.
- **Other Time Functions**:
- `CURRENT_DATE`: Returns the current date only (no time).
- `CURRENT_TIME`: Returns the current time of day.
- `NOW()`: Another way to get the current date and time.
---
### **3. Syntax Without Naming the Constraint**
If you don???t need to name the default constraint explicitly, you can define the `DEFAULT` directly in the column definition:
```sql
CREATE TABLE accounts (
account_id SERIAL PRIMARY KEY,
billing_date TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP
);
```
---
### **4. Adding a Default Constraint to an Existing Table**
You can add a default constraint to a column after the table is created. However, naming the constraint explicitly isn't directly supported in this syntax:
```sql
ALTER TABLE accounts
ALTER COLUMN billing_date SET DEFAULT CURRENT_TIMESTAMP;
```
To manage the default constraint as a named object, PostgreSQL recommends explicitly creating the constraint when defining the table.
---
### **5. Dropping a Default Constraint**
In PostgreSQL, the `DEFAULT` value is part of the column definition rather than a separately named constraint, so you drop it using the `ALTER COLUMN` syntax:
```sql
ALTER TABLE accounts
ALTER COLUMN billing_date DROP DEFAULT;
```
---
### **6. Complete Table Example**
Here???s an example that mimics SQL Server's style with a named `DEFAULT` constraint:
```sql
CREATE TABLE accounts (
account_id SERIAL PRIMARY KEY,
billing_date TIMESTAMP(3) NOT NULL
CONSTRAINT DF_Account_BillingDate DEFAULT CURRENT_TIMESTAMP,
balance NUMERIC(10, 2) NOT NULL
CONSTRAINT DF_Account_Balance DEFAULT 0.00
);
```
---
### **7. Key Differences Between PostgreSQL and SQL Server**
| Feature | SQL Server | PostgreSQL |
|-----------------------------------|------------------------------------------------|--------------------------------------------|
| **Default Constraint Naming** | Named explicitly or generated automatically | Must be explicitly named |
| **System Functions** | `GETDATE()` | `CURRENT_TIMESTAMP` or `NOW()` |
| **Constraint Management** | Default constraints are separate objects | Default is part of the column definition |
| **Dropping Default Constraints** | `ALTER TABLE DROP CONSTRAINT` | `ALTER COLUMN DROP DEFAULT` |
---
### **8. Constraints vs. Defaults**
In PostgreSQL, a `DEFAULT` value is typically treated as part of the column definition rather than a separate constraint. Explicit naming is optional but good for documentation and clarity when the schema is complex.
### **Conclusion**
Yes, you can explicitly name default constraints in PostgreSQL, just like in SQL Server. The syntax requires the `CONSTRAINT` keyword before the `DEFAULT` clause. However, PostgreSQL treats defaults as part of the column definition rather than standalone objects, so naming them is less common unless you have specific reasons to manage them explicitly.
Author: user
does PostGres have an equivalent of extended_proprties to describe the tables with comments?
Author: ChatGPT
Yes, PostgreSQL provides a feature equivalent to SQL Server's `sys.extended_properties` for adding descriptive metadata to database objects: **comments**. You can use the `COMMENT` command to add descriptions to tables, columns, schemas, functions, and other database objects.
---
### **1. Adding Comments to Tables and Columns**
#### **Syntax**
- To comment on a table:
```sql
COMMENT ON TABLE table_name IS 'Description of the table';
```
- To comment on a column:
```sql
COMMENT ON COLUMN table_name.column_name IS 'Description of the column';
```
#### **Example**
```sql
-- Add a comment to a table
COMMENT ON TABLE accounts IS 'This table stores account information';
-- Add a comment to a column
COMMENT ON COLUMN accounts.account_id IS 'Primary key for the accounts table';
COMMENT ON COLUMN accounts.billing_date IS 'Date when the account is billed';
```
---
### **2. Retrieving Comments**
PostgreSQL stores comments in the `pg_description` and `pg_shdescription` system catalog tables. These tables can be queried to retrieve comments.
#### **Querying Table Comments**
- Retrieve comments for tables:
```sql
SELECT obj_description(oid, 'pg_class') AS comment, relname AS table_name
FROM pg_class
WHERE relkind = 'r' AND relname = 'accounts';
```
- Retrieve comments for all columns in a table:
```sql
SELECT
col_description(a.attrelid, a.attnum) AS column_comment,
a.attname AS column_name
FROM pg_catalog.pg_attribute a
WHERE a.attrelid = 'accounts'::regclass AND a.attnum > 0 AND NOT a.attisdropped;
```
---
### **3. Comparison with SQL Server's `extended_properties`**
| Feature | SQL Server (`sys.extended_properties`) | PostgreSQL (`COMMENT`) |
|------------------------------------|-----------------------------------------------------|--------------------------------------------|
| **Usage** | Add metadata to tables, columns, etc. | Add descriptions to tables, columns, etc. |
| **Storage** | Stored in `sys.extended_properties` | Stored in `pg_description` or `pg_shdescription` |
| **Retrieval** | Query `sys.extended_properties` | Query `pg_description` using functions like `col_description` or `obj_description` |
| **Object Support** | Tables, columns, schemas, constraints, indexes, etc.| Tables, columns, schemas, functions, etc. |
| **Syntax** | `EXEC sp_addextendedproperty ...` | `COMMENT ON ... IS ...` |
---
### **4. Adding Comments to Other Objects**
You can add comments to various other database objects in PostgreSQL, including:
- **Indexes:**
```sql
COMMENT ON INDEX accounts_idx IS 'Index on the accounts table';
```
- **Schemas:**
```sql
COMMENT ON SCHEMA public IS 'Default schema for the database';
```
- **Constraints:**
```sql
COMMENT ON CONSTRAINT pk_accounts ON accounts IS 'Primary key constraint for accounts';
```
- **Functions:**
```sql
COMMENT ON FUNCTION calculate_total(integer) IS 'Calculates the total amount';
```
---
### **5. Notes**
- **Comment Persistence:** Comments are stored in the database metadata and persist across sessions and restarts.
- **Default Comments:** Objects without explicit comments will return `NULL` when queried.
- **Updating Comments:** Simply run the `COMMENT ON` command again to overwrite the existing comment.
- **Deleting Comments:** Use `COMMENT ON ... IS NULL` to remove a comment:
```sql
COMMENT ON TABLE accounts IS NULL;
```
---
### **Conclusion**
PostgreSQL's `COMMENT` system provides a straightforward way to add descriptive metadata to database objects, similar to SQL Server's `sys.extended_properties`. While not as complex or extensible as `extended_properties`, it is well-integrated into PostgreSQL's ecosystem and sufficient for most documentation needs.
Author: user
In PostGres, is there an equivilent for SLq Server Compression, like CREATE NONCLUSTERED INDEX "IX2_Account"
ON "Account" ("GroupID" , "AccountID" ) WITH (DATA_COMPRESSION = PAGE );
Author: ChatGPT
PostgreSQL does not have a direct equivalent of SQL Server's `DATA_COMPRESSION` feature for indexes or tables. However, PostgreSQL does provide various mechanisms for reducing storage requirements and optimizing performance, which serve similar purposes as compression.
Here???s how PostgreSQL approaches compression and storage optimization:
---
### **1. Storage-Level Compression**
#### **a. TOAST (The Oversized-Attribute Storage Technique)**
- PostgreSQL automatically compresses large values using TOAST for fields that exceed a certain size.
- Compression is applied at the column level for data types like `TEXT`, `BYTEA`, and `JSONB`.
- Default compression algorithm: **lz4** (from PostgreSQL 14) or **pglz** (older versions).
- Example:
```sql
CREATE TABLE accounts (
account_id SERIAL PRIMARY KEY,
group_id INT,
account_name TEXT,
details TEXT
);
```
If `details` is large enough, it will automatically be compressed using TOAST.
- **Control TOAST Compression**:
You can set the `COMPRESSION` method for a column:
```sql
ALTER TABLE accounts ALTER COLUMN details SET COMPRESSION lz4;
```
---
### **2. Index-Level Optimization**
#### **a. Index Types**
PostgreSQL provides several index types, and choosing the right one can reduce storage and improve query performance:
- **B-Tree** (default): Optimized for general-purpose indexing.
- **GIN** (Generalized Inverted Index): Effective for full-text search and JSONB fields.
- **GiST**: Useful for spatial data.
- **BRIN** (Block Range Index): Very space-efficient for large tables with sequentially correlated data.
#### **b. Index Compression**
PostgreSQL supports **deduplication** in B-Tree indexes (from PostgreSQL 13), which reduces the storage space required for duplicate values.
- Deduplication occurs automatically for indexes where duplicate keys are common:
```sql
CREATE INDEX ix_account_groupid_accountid
ON account (group_id, account_id);
```
---
### **3. Columnar Storage and Compression**
PostgreSQL does not natively support columnar storage, but extensions like **cstore_fdw** and **TimescaleDB** provide columnar storage with compression:
- **cstore_fdw**: Enables columnar storage for analytical queries.
- **TimescaleDB**: Built on PostgreSQL, offering advanced time-series data compression.
#### Example with `TimescaleDB`:
```sql
-- Add the TimescaleDB extension
CREATE EXTENSION IF NOT EXISTS timescaledb;
-- Create a table with compression
SELECT add_compression_policy('table_name', INTERVAL '7 days');
```
---
### **4. Table and Tablespace Compression**
While PostgreSQL doesn't offer table-level compression, you can compress tables at the filesystem level:
- Use a compressed tablespace:
```bash
mount -o compress=lz4 /path/to/tablespace
```
- Then create a tablespace on that filesystem:
```sql
CREATE TABLESPACE compressed_space LOCATION '/path/to/tablespace';
CREATE TABLE accounts TABLESPACE compressed_space;
```
---
### **5. WAL Compression**
PostgreSQL supports Write-Ahead Logging (WAL) compression to reduce the size of WAL logs:
- Enable WAL compression in `postgresql.conf`:
```ini
wal_compression = on
```
---
### **6. Compression Extensions**
Several PostgreSQL extensions provide advanced compression:
- **pg_compression**: Adds custom compression methods.
- **zheap**: A storage engine that supports table-level compression.
- **citus**: Enables distributed database compression.
---
### **Comparison: SQL Server vs. PostgreSQL Compression**
| Feature | SQL Server Compression | PostgreSQL Equivalent |
|----------------------------------|---------------------------------------------|-----------------------------------------|
| **Row and Page Compression** | `DATA_COMPRESSION = ROW/PAGE` | Automatic compression via TOAST |
| **Index Compression** | `DATA_COMPRESSION` for indexes | B-Tree deduplication (automatic) |
| **Table-Level Compression** | Supported | Extensions (e.g., `cstore_fdw`) |
| **Columnar Storage** | `CLUSTERED COLUMNSTORE INDEX` | Extensions (`cstore_fdw`, `TimescaleDB`)|
| **WAL Compression** | Not directly equivalent | `wal_compression = on` |
| **Filesystem-Level Compression** | Not integrated | Use compressed tablespaces |
---
### **Conclusion**
PostgreSQL doesn???t have an exact equivalent to SQL Server???s `DATA_COMPRESSION` syntax for indexes or tables. However, it provides various compression mechanisms at the column level (TOAST), deduplication for B-Tree indexes, and extensibility for advanced compression techniques. Depending on your use case, PostgreSQL can achieve similar outcomes through these features and extensions.