Declare variable in SQLite and use it

问题

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

Like in MS SQL:

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

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

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

回答1:

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

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;
    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;

回答2:

Herman's solution works, but it can be simplified because Sqlite allows to store any value type on any field.

Here is a simpler version that uses one Value field declared as TEXT to store any value:

CREATE TEMP TABLE IF NOT EXISTS Variables (Name TEXT PRIMARY KEY, Value TEXT);

INSERT OR REPLACE INTO Variables VALUES ('VarStr', 'Val1');
INSERT OR REPLACE INTO Variables VALUES ('VarInt', 123);
INSERT OR REPLACE INTO Variables VALUES ('VarBlob', x'12345678');

SELECT Value
  FROM Variables
 WHERE Name = 'VarStr'
UNION ALL
SELECT Value
  FROM Variables
 WHERE Name = 'VarInt'
UNION ALL
SELECT Value
  FROM Variables
 WHERE Name = 'VarBlob';

回答3:

Herman's solution worked for me, but the ... had me mixed up for a bit. I'm including the demo I worked up based on his answer. The additional features in my answer include foreign key support, auto incrementing keys, and use of the last_insert_rowid() function to get the last auto generated key in a transaction.

My need for this information came up when I hit a transaction that required three foreign keys but I could only get the last one with last_insert_rowid().

PRAGMA foreign_keys = ON;   -- sqlite foreign key support is off by default
PRAGMA temp_store = 2;      -- store temp table in memory, not on disk

CREATE TABLE Foo(
    Thing1 INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL
);

CREATE TABLE Bar(
    Thing2 INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    FOREIGN KEY(Thing2) REFERENCES Foo(Thing1)
);

BEGIN TRANSACTION;

CREATE TEMP TABLE _Variables(Key TEXT, Value INTEGER);

INSERT INTO Foo(Thing1)
VALUES(2);

INSERT INTO _Variables(Key, Value)
VALUES('FooThing', last_insert_rowid());

INSERT INTO Bar(Thing2)
VALUES((SELECT Value FROM _Variables WHERE Key = 'FooThing'));

DROP TABLE _Variables;

END TRANSACTION;

回答4:

For a read-only variable (that is, a constant value set once and used anywhere in the query), use a Common Table Expression (CTE).

WITH const AS (SELECT 'name' AS name, 10 AS more)
SELECT *, (table.cost + const.more) AS newCost
FROM table, const 
WHERE table.name = const.name

SQLite WITH clause

回答5:

Try using Binding Values. You cannot use variables as you do in T-SQL but you can use "parameters". I hope the following link is usefull.Binding Values

来源：https://stackoverflow.com/questions/7739444/declare-variable-in-sqlite-and-use-it

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sql

sqlite

variables

declaration