[英]Why does this SQLite UPDATE statement write changes to all records in the table?
This query returns 40319 records:此查询返回 40319 条记录:
SELECT artist,
title,
composer AS alib_composer,
master.composer AS master_composer
FROM alib
INNER JOIN
master ON hex(alib.__path) = hex(master.__path) AND
alib.l_title = lower(master.title) AND
alib.composer != master.composer AND
length(alib.composer) != length(master.composer) AND
master.composer LIKE "% %" AND
alib.composer NOT LIKE "% %";
Translating above into the following UPDATE query results in all records in alib being updated.将以上转换为以下 UPDATE 查询会导致 alib 中的所有记录都被更新。 Could someone help me understand why this is the case?
有人能帮我理解为什么会这样吗?
UPDATE alib
SET composer = (
SELECT composer
FROM master
WHERE hex(alib.__path) = hex(master.__path) AND
alib.l_title = lower(master.title) AND
alib.composer != master.composer AND
length(alib.composer) != length(master.composer) AND
master.composer LIKE "% %" AND
alib.composer NOT LIKE "% %"
);
I suspect I know why, but turning the update into something like this:我怀疑我知道为什么,但将更新变成这样:
UPDATE alib
SET composer = master.composer
WHERE hex(alib.__path) = hex(master.__path) AND
alib.l_title = lower(master.title) AND
alib.composer != master.composer AND
length(alib.composer) != length(master.composer) AND
master.composer LIKE "% %" AND
alib.composer NOT LIKE "% %";
causes SQLite to complain:导致 SQLite 抱怨:
Error while executing SQL query on database 'x': no such column: master.composer
Because there is no WHERE clause on the outer/main UPDATE SQL ie it is basiclly因为外部/主 UPDATE SQL 上没有 WHERE 子句,即它基本上是
UPDATE alib SET composer = the_result_of_the_subquery;
You want a WHERE clause to say which rows to update along the lines of :-您需要一个 WHERE 子句来说明要更新的行:-
UPDATE alib SET composer = the_result_of_the_subquery WHERE ??????;
Or to use your code :-或者使用您的代码:-
UPDATE alib
SET composer = (
SELECT composer
FROM master
WHERE hex(alib.__path) = hex(master.__path) AND
alib.l_title = lower(master.title) AND
alib.composer != master.composer AND
length(alib.composer) != length(master.composer) AND
master.composer LIKE "% %" AND
alib.composer NOT LIKE "% %"
)
WHERE the_expression_to_restrict_which_rows_are_updated
;
This hasn't been fully tested but this may be solution you are looking for :-这尚未经过全面测试,但这可能是您正在寻找的解决方案:-
WITH cte AS
(
SELECT
master.composer AS master_composer,
alib.rowid AS arowid
FROM alib
INNER JOIN
master ON hex(alib.__path) = hex(master.__path)
AND alib.l_title = lower(master.title)
AND alib.composer != master.composer
AND length(alib.composer) != length(master.composer)
AND master.composer LIKE '% %'
AND alib.composer NOT LIKE '% %'
)
UPDATE alib
SET composer =
(
SELECT cte.master_composer FROM cte WHERE cte.arowid = alib.rowid
)
WHERE alib.rowid IN (SELECT arowid FROM cte);
The following SQL was used for testing :-以下 SQL 用于测试:-
DROP TABLE IF EXISTS alib;
DROP TABLE IF EXISTS master;
CREATE TABLE IF NOT EXISTS alib (__path,l_title,composer);
CREATE TABLE IF NOT EXISTS master (__path,title,artist,composer);
INSERT INTO alib VALUES
('path1','this','bert'),
('path2','something else','Joe'),
('path2','something else','Joe'), -- duplicate likely irrelevant but still updated
('path2','something else','Joe Someone'), -- already has space in composer skipped
('path100','an so on','x') -- no equivalent in master
;
INSERT INTO master VALUES
('path1','this','fred','bert'), -- ignored as no space
('path1','this','fred bloggs','Julia smith'),
('path2','something else','Alison','Joe Brown')
;
/* DEMO OF EXTRACTED ROWS */
WITH cte AS
(
SELECT
master.composer AS master_composer,
alib.rowid AS arowid
FROM alib
INNER JOIN
master ON hex(alib.__path) = hex(master.__path)
AND alib.l_title = lower(master.title)
AND alib.composer != master.composer
AND length(alib.composer) != length(master.composer)
AND master.composer LIKE '% %'
AND alib.composer NOT LIKE '% %'
)
SELECT * FROM cte;
WITH cte AS
(
SELECT
master.composer AS master_composer,
alib.rowid AS arowid
FROM alib
INNER JOIN
master ON hex(alib.__path) = hex(master.__path)
AND alib.l_title = lower(master.title)
AND alib.composer != master.composer
AND length(alib.composer) != length(master.composer)
AND master.composer LIKE '% %'
AND alib.composer NOT LIKE '% %'
)
UPDATE alib
SET composer =
(
SELECT cte.master_composer FROM cte WHERE cte.arowid = alib.rowid
)
WHERE alib.rowid IN (SELECT arowid FROM cte);
SELECT * FROM alib;
DROP TABLE IF EXISTS alib;
DROP TABLE IF EXISTS master;
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