使用：
SELECt t1.*, COALESCE(x.num_rows, 0) AS entries FROM `table 1` t1LEFT JOIN (SELECt t3.v_id, COUNT(*) 'num_rows' FROM `table_3` t3 GROUP BY t3.v_id) x ON x.v_id = t1.v_id
使用：
SELECt t1.*, COALESCE(x.num_rows, 0) AS entries FROM `table 1` t1LEFT JOIN (SELECt t3.v_id, COUNT(*) 'num_rows' FROM `table_3` t3 GROUP BY t3.v_id) x ON x.v_id = t1.v_id
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