在 SQLite 中声明变量并使用它

2021-12-08 00:00:00 sql variables sqlite declaration

我想在 SQLite 中声明一个变量并在 insert 操作中使用它.

I want to declare a variable in SQLite and use it in insert operation.

就像在 MS SQL 中一样:

Like in MS SQL:

declare @name as varchar(10)
set name = 'name'
select * from table where name = @name

例如，我需要获取 last_insert_row 并在 insert 中使用它.

For example, I will need to get last_insert_row and use it in insert.

我发现了一些关于绑定的东西，但我并没有完全理解它.

I have found something about binding but I didn't really fully understood it.

推荐答案

SQLite 不支持本机变量语法，但您可以使用内存中的临时表实现几乎相同的效果.

SQLite doesn't support native variable syntax, but you can achieve virtually the same using an in-memory temp table.

我已经在大型项目中使用了以下方法并且效果很好.

I've used the below approach for large projects and works like a charm.

    /* Create in-memory temp table for variables */
    BEGIN;

    PRAGMA temp_store = 2; /* 2 means use in-memory */
    CREATE TEMP TABLE _Variables(Name TEXT PRIMARY KEY, RealValue REAL, IntegerValue INTEGER, BlobValue BLOB, TextValue TEXT);

    /* Declaring a variable */
    INSERT INTO _Variables (Name) VALUES ('VariableName');

    /* Assigning a variable (pick the right storage class) */
    UPDATE _Variables SET IntegerValue = ... WHERE Name = 'VariableName';

    /* Getting variable value (use within expression) */
    ... (SELECT coalesce(RealValue, IntegerValue, BlobValue, TextValue) FROM _Variables WHERE Name = 'VariableName' LIMIT 1) ...

    DROP TABLE _Variables;
    END;

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