Скачать или смотреть Join All Tables in PostgreSQL Dynamically with a Unique Source Column

Discover how to dynamically join all tables in a PostgreSQL database that share the same structure without specifying each table name individually.
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Joining All Tables in PostgreSQL Dynamically: A Step-by-Step Guide

In a complex database scenario, you may find yourself with multiple tables all containing the same columns and data types, yet each table has to remain distinct. This is a common requirement in many data management situations. But how can you handle the challenge of dynamically joining all these tables when their names may change over time? Let's explore a solution that automates this joining process efficiently.

The Challenge

Imagine you have a database named all_data with several tables like red and green, each featuring identical columns:

Columns: date text, value numeric, notes text

Your goal is to create a query that finds all those tables, joins them, and labels them appropriately with the respective source table name. For instance, your output should look something like this:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To address this question, we'll create a dynamic query in PostgreSQL. This query will automatically find and join all the tables that meet your criteria without needing you to specify each table by name.

Step 1: Generating the Dynamic Query

First, we will construct a query that combines all relevant SELECT statements into a single SQL execution. Here’s how you can achieve that:

[[See Video to Reveal this Text or Code Snippet]]

Explanation:

information_schema.tables: This system view contains the metadata of all tables in the database.

string_agg: This function concatenates the strings generated for each table, creating the complete UNION statement.

regexp_replace: This part of the query ensures that the trailing UNION ALL is removed from the final assembled SQL.

Step 2: Examining the Output

When executed, the dynamic SQL will yield results similar to:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Creating a PL/pgSQL Function

To simplify future use of this dynamic query, creating a PL/pgSQL function would be beneficial. Here’s an example of how such a function could be constructed:

[[See Video to Reveal this Text or Code Snippet]]

Function Breakdown:

Cursor: This retrieves names of the tables dynamically from the information_schema.tables.

Loop: Every table name is processed, and a SELECT statement is executed returning the data with the source label.

Step 4: Invoking the Function

After creating the function, you can easily get consolidated results by calling it:

[[See Video to Reveal this Text or Code Snippet]]

This will retrieve all data from the specified tables in the desired format efficiently.

Conclusion

By implementing a dynamic query and creating a reusable PL/pgSQL function, you can efficiently manage and consolidate data from multiple tables in your PostgreSQL database. This approach minimizes the manual overhead and keeps your database interactions streamlined and adaptable to changes.

Now, you can focus on analyzing your data instead of worrying about rewriting queries every time your database schema changes!