在筛选查询中,exists通常用于判断某个字段是否存在,常见的应用包括:
SELECT * FROM table_name
WHERE EXISTS (SELECT 1 FROM another_table WHERE condition);
SELECT column_name
FROM table_name
WHERE EXISTS (SELECT column_name FROM another_table WHERE condition);
SELECT * FROM table_name
WHERE EXISTS (SELECT column_name FROM another_table WHERE column_name IS NOT NULL);
SELECT column_name
FROM table_name
WHERE EXISTS (SELECT column_name FROM another_table WHERE table_name.id = another_table.id);
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