[英]MySQL - How to count entries in one table based on criteria in another table (except when)
[英]Deleting table entries based on criteria in another table
我們希望能夠根據在另一個表中設置的刪除標准從 MySQL 表中刪除條目。 讓我用一個例子來解釋。
我有兩個表定義如下:
CREATE TABLE base_tbl
(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
f1 VARCHAR(8),
f2 VARCHAR(8),
PRIMARY KEY (id)
);
CREATE TABLE del_criteria_tbl
(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
f3 VARCHAR(8),
f4 VARCHAR(8),
PRIMARY KEY (id)
);
base_tbl
具有數據,而del_criteria_tbl
具有從base_tbl
中刪除條目的標准。
我按如下方式填充表格:
INSERT INTO base_tbl(f1, f2) VALUES ('ABC', '123C57'),
('ABC', '532B49'), ('DEF', '397F45'),
('DEF', '684G65'), ('GHI', '793A86'),
('GHI', '541H32');
和
INSERT INTO del_criteria_tbl(f3, f4) VALUES ('ABC', '532B49'),
('ABC', '813E89'), ('DEF', '397F45'),
('GHI', '541H32');
明顯地:
mysql>SELECT * FROM base_tbl;
+----+------+--------+
| id | f1 | f2 |
+----+------+--------+
| 1 | ABC | 123C57 |
| 2 | ABC | 532B49 |
| 3 | DEF | 397F45 |
| 4 | DEF | 684G65 |
| 5 | GHI | 793A86 |
| 6 | GHI | 541H32 |
+----+------+--------+
mysql>SELECT * FROM del_criteria_tbl;
+----+------+--------+
| id | f3 | f4 |
+----+------+--------+
| 1 | ABC | 532B49 |
| 2 | ABC | 813E89 |
| 3 | DEF | 397F45 |
| 4 | GHI | 541H32 |
+----+------+--------+
我想定義一個簡潔高效的 SQL 操作,執行如下偽 SQL 邏輯:
DELETE FROM base_tbl WHERE base_tbl.f1 = del_criteria_tbl.f3 AND base_tbl.f2 = del_criteria_tbl.f4
操作執行后, SELECT * FROM base_tbl
應該產生:
+----+------+--------+
| id | f1 | f2 |
+----+------+--------+
| 1 | ABC | 123C57 |
| 4 | DEF | 684G65 |
| 5 | GHI | 793A86 |
+----+------+--------+
一個簡單的方法是IN
:
DELETE b FROM base_tbl b
WHERE (b.f1, b.f2) IN (SELECT dc.f3, dc.f4
FROM del_criteria_tbl dc
);
使用(f1, f2)
上的索引,您可能會發現JOIN
具有更好的性能:
DELETE b
FROM base_tbl b JOIN
del_criteria_tbl dc
ON b.f1 = dc.f3 AND b.f2 = c.f4;
我會推薦exists
:
delete b
from base_tbl b
where exists (
select 1
from del_criteria_tbl dc
where dc.f1 = b.f1 and dc.f2 = b.f2
)
這似乎是表達您要求的最自然的方式。 exists
通常比in
大型數據集中更好地擴展。 為了提高性能,您需要del_criteria_tbl(f1, f2)
上的索引。
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