Given scenarios, write queries to validate data.
💡 Model Answer
For each scenario, identify the key validation rule. 1) Row count consistency: SELECT COUNT() FROM table1; SELECT COUNT() FROM table2; 2) Primary key uniqueness: SELECT key_col, COUNT() FROM table GROUP BY key_col HAVING COUNT() > 1; 3) Referential integrity: SELECT t1.id FROM table1 t1 LEFT JOIN table2 t2 ON t1.id = t2.ref_id WHERE t2.ref_id IS NULL; 4) Data type and range checks: SELECT * FROM table WHERE numeric_col NOT BETWEEN 0 AND 100; 5) Checksum comparison: SELECT MD5(GROUP_CONCAT(col1, col2 ORDER BY id)) AS chk FROM table; Compare chk across environments. These queries provide quick sanity checks and help catch migration or integration errors.
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