Question

我发现查询计划在w / o和w / keys之间改变。

CREATE TABLE `data` (
    `name`  TEXT,
    `value` NUMERIC,
    PRIMARY KEY(`name`)
) WITHOUT ROWID;

CREATE TABLE `ranges` (
    `begin` TEXT,
    `end`   TEXT,
);

explain query plan select distinct t1.name as name from data t1, ranges t2 where t1.name between t2.begin and t2.end order by name;

"0" "0" "1" "SCAN TABLE ranges AS t2"
"0" "1" "0" "SEARCH TABLE data AS t1 USING PRIMARY KEY (name>? AND name<?)"
"0" "0" "0" "USE TEMP B-TREE FOR DISTINCT"

如果我将开始和结束定义为键，

CREATE TABLE `ranges` (
    `begin` TEXT,
    `end`   TEXT,
    PRIMARY KEY(`begin`,`end`)
);

查询计划更改为以下内容。

"0" "0" "0" "SCAN TABLE data AS t1"
"0" "1" "1" "SEARCH TABLE ranges AS t2 USING COVERING INDEX sqlite_autoindex_ranges_1 (begin<?)"

第一个查询计划更好，因为在我的情况下，数据表比范围大得多。

我读了https://sqlite.org/optoverview.html。它表示连接顺序是由sqlite的默认选择（没有分析结果）定义的。添加这些键是否会更改默认选项？有没有其他技巧让SQLite使用第一个查询计划而不提供统计数据？

另外，默认选择是否未更改？以后会改变吗？我用3.22。

我还注意到，如果我不使用order by和distinct，它总是使用第一个计划

explain query plan select t1.name as name from data t1, ranges t2 where t1.name between t2.begin and t2.end;

"0" "0" "1" "SCAN TABLE ranges AS t2"
"0" "1" "0" "SEARCH TABLE data AS t1 USING PRIMARY KEY (name>? AND name<?)"

表连接顺序在w /和w / o键之间改变

0 个答案: