When to use: Use UNION or UNION ALL to combine rows from two or more queries (i.e., results of two separate SELECT statements) into a single result set. The tables involved should have the same structure (same number of columns and data types), but they don’t need to be related by a key or condition.
SELECT name FROM table1 UNION SELECT name FROM table2;
SET ကို Query — ၂ ခုက ရတဲ့ ရလဒ်တွေကို ပေါင်းစည်းချင်တဲ့အခါ အသုံးပြုပါတယ်။ ဒီနေရာမှာ သတိထားရမှာက data type အမျိုးအစားတူရမှာ ဖြစ်ပါတယ်။
Return all records from both Queries: No — duplicate
Return records from both Queries: With duplicates
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Summary
JOIN Operations (INNER JOIN, LEFT JOIN, etc.)
When to use: Use JOIN to combine related data from two or more tables based on a condition, typically a common column between the tables (e.g., a foreign key relationship).
SELECT employees.name, departments.name FROM employees INNER JOIN departments ON employees.dept_id = departments.id;
