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Question

如何获取连接子查询为空的行？

SELECT *
FROM bank_recon b
LEFT JOIN (
    SELECT o.bank_recon_id
    FROM data_voucher_ocr_bank o
    LEFT JOIN data_voucher v ON v.id=o.data_voucher_id
    WHERE v.is_ocr_verified=1
    LIMIT 1
) s ON s.bank_recon_id=b.id
WHERE s IS NULL

更新

使用此查询（子查询）时，会根据是否设置is_ocr_verified来提取某些内容

SELECT o.bank_recon_id
FROM data_voucher_ocr_bank o
LEFT JOIN data_voucher v ON v.id=o.data_voucher_id
WHERE v.is_ocr_verified=1 && o.bank_recon_id=320062

使用此查询时，无论如何都会获取所有内容！？

SELECT b.txt, b.amount
FROM bank_recon b
LEFT JOIN (
    SELECT o.bank_recon_id
    FROM data_voucher_ocr_bank o
    LEFT JOIN data_voucher v ON v.id=o.data_voucher_id
    WHERE v.is_ocr_verified=1
    LIMIT 1
) s ON s.bank_recon_id=b.id
WHERE b.id=320062 && s.bank_recon_id IS NULL

Answer 1

在WHERE子句中指定一个列，而不仅仅是子查询。

WHERE s.bank_recon_id IS NULL

Answer 2

反连接（这是您尝试在此处应用的）是我们在直接NOT IN或NOT EXISTS在DBMS中存在性能问题时使用的方法。

如果data_voucher_ocr_bank.bank_recon_id不能为空，我们可以使用：

SELECT txt, amount
FROM bank_recon
WHERE id NOT IN
(
  SELECT bank_recon_id
  FROM data_voucher_ocr_bank
  WHERE data_voucher_id IN (SELECT id FROM data_voucher WHERE is_ocr_verified = 1)
);

（否则我们会添加AND bank_recon_id IS NOT NULL或使用NOT EXISTS。）

获取左连接子查询为空（未找到）的行

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2 个答案: