When working with Snowflake, there might be scenarios where you need to compare two tables to determine differences. These differences might be at the level of structure (columns) or at the data level (rows).
1. Compare Structures of Two Tables
To determine if the tables have the same structure:
SELECT COLUMN_NAME, DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'YOUR_FIRST_TABLE' AND TABLE_SCHEMA = 'YOUR_SCHEMA' EXCEPT SELECT COLUMN_NAME, DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'YOUR_SECOND_TABLE' AND TABLE_SCHEMA = 'YOUR_SCHEMA';
If the result is empty, the structures match. Otherwise, the result will show differences.
2. Compare data between two tables
To check if two tables have the same data, you can use a FULL OUTER JOIN to find differences. Assuming tables table_A and table_B:
SELECT * FROM table_A FULL OUTER JOIN table_B ON table_A.primary_key = table_B.primary_key WHERE table_A.primary_key IS NULL OR table_B.primary_key IS NULL;
The result will show rows that are in one table but not in the other. Adjust the join conditions as needed based on your tables.
For comparing all columns:
SELECT * FROM table_A a FULL OUTER JOIN table_B b ON a.primary_key = b.primary_key WHERE NOT EXISTS ( SELECT a.* EXCEPT SELECT b.* );
3. Count rows in both tables
Simple row counts can also give insights:
SELECT (SELECT COUNT(*) FROM table_A) AS table_A_count, (SELECT COUNT(*) FROM table_B) AS table_B_count;
4. Check for exact row matches
If you want to determine if every row in
table_A matches a row in
SELECT COUNT(*) FROM table_A MINUS SELECT COUNT(*) FROM table_B;