Question

我有一个包含邮政编码的数据库表，city，long，lat，省。

我有一个用于此表的用途，用于返回自动完成小部件的建议代码（加上城市和省份）。

city和postalcode组成了一张独特的记录。我以3个字符开始查询。

此查询速度很慢，导致自动填充体验不佳。我想知道上面的信息什么样的索引最好？我正在使用Azure SQL数据存储区，因此我无法运行查询分析器/调优顾问。

我在postalCode上尝试了非聚集索引，在postalCode和city上尝试了2列聚簇索引。两者都在查询中产生相同的结果：

Select * 
From PostalCode 
Where code LIKE '%L6J 0%'

我没有更新或插入此表。

Answer 1

由于邮政编码的长度相当短且已知（8），因此这是一个很好的分块选择。将邮政编码分解为所有组成块并将它们与起始位置和长度一起存储以启用索引搜索。

例如，对于像'OX1 1JZ'这样的邮政编码，请存储以下所有字符串：

start len postcodePart
1   2   OX
1   3   OX1
1   4   OX11
1   5   OX11J
1   6   OX11JZ
2   2   X1
2   3   X11
2   4   X11J
2   5   X11JZ
3   2   11
3   3   11J
3   4   11JZ
4   2   1J
4   3   1JZ
5   2   JZ

这是一个示例脚本，演示了该技术以及如何使用100个样本邮政编码和触发器来粉碎邮政编码。

NB !! 这不是生产就绪代码，只是展示技术的示例。

USE tempdb
GO

-- https://www.postcodelist.co.uk/
--uk-postcodes.csv

IF OBJECT_ID('dbo.postCodeParts') IS NOT NULL DROP TABLE dbo.postCodeParts
IF OBJECT_ID('dbo.postCodes') IS NOT NULL DROP TABLE dbo.postCodes
GO

CREATE TABLE dbo.postCodes (
    postcodeId              INT IDENTITY CONSTRAINT PK_postCodes PRIMARY KEY,
    postcode                VARCHAR(8) NOT NULL

    --... the rest of your columns

    )
GO


CREATE TABLE dbo.postCodeParts (
    postcodePartId          INT IDENTITY CONSTRAINT PK_postCodeParts PRIMARY KEY NONCLUSTERED,
    postcodeId              INT NOT NULL FOREIGN KEY REFERENCES dbo.postCodes ( postcodeId ),

    totalLen                TINYINT NOT NULL,
    xStart                  TINYINT NOT NULL,
    xLen                    TINYINT NOT NULL,
    postcodePart            VARCHAR(8) NOT NULL INDEX cdx_postCodeParts CLUSTERED

    )
GO


-- Add a trimmed copy of the postcode to the parts table, chunked up.
CREATE TRIGGER dbo.trg_postCodes
ON dbo.postcodes
FOR INSERT
AS
BEGIN

    ;WITH cte AS
    (
    SELECT *
    FROM (
        VALUES ( 1 ), ( 2 ), ( 3 ), ( 4 ), ( 5 ), ( 6 ), ( 7 ), ( 8 ) 
        ) x(y)
    )
    INSERT INTO dbo.postCodeParts ( postcodeId, totalLen, xStart, xLen, postcodePart )
    SELECT 
        p.postcodeId, 
        p.xTotalLen, 
        c1.y AS xstart, 
        c2.y AS xlen, 
        SUBSTRING( p.postCode, c1.y, c2.y ) AS xstring
    FROM ( 
        SELECT
            postcodeId,
            REPLACE( postcode, ' ', '' ) postCode, 
            LEN( REPLACE( postcode, ' ', '' ) ) AS xTotalLen 
        FROM inserted 
    ) p
        CROSS JOIN cte c1
            CROSS JOIN cte c2
    WHERE c2.y Between 2 And p.xTotalLen
      AND ( ( c2.y ) + ( c1.y - 1 ) ) <= p.xTotalLen

END
GO


INSERT INTO dbo.postcodes ( postcode )
VALUES
    ( 'OX1 1AA' ),( 'OX1 1AB' ),( 'OX1 1AD' ),( 'OX1 1AE' ),( 'OX1 1AF' ),( 'OX1 1AG' ),( 'OX1 1AN' ),( 'OX1 1AS' ),( 'OX1 1AW' ),( 'OX1 1AY' ),
    ( 'OX1 1AZ' ),( 'OX1 1BD' ),( 'OX1 1BE' ),( 'OX1 1BN' ),( 'OX1 1BP' ),( 'OX1 1BS' ),( 'OX1 1BT' ),( 'OX1 1BU' ),( 'OX1 1BX' ),( 'OX1 1BY' ),
    ( 'OX1 1BZ' ),( 'OX1 1DA' ),( 'OX1 1DB' ),( 'OX1 1DE' ),( 'OX1 1DF' ),( 'OX1 1DG' ),( 'OX1 1DJ' ),( 'OX1 1DL' ),( 'OX1 1DP' ),( 'OX1 1DQ' ),
    ( 'OX1 1DS' ),( 'OX1 1DW' ),( 'OX1 1DZ' ),( 'OX1 1EA' ),( 'OX1 1EF' ),( 'OX1 1EJ' ),( 'OX1 1EN' ),( 'OX1 1EP' ),( 'OX1 1EQ' ),( 'OX1 1ER' ),
    ( 'OX1 1ES' ),( 'OX1 1ET' ),( 'OX1 1EU' ),( 'OX1 1EW' ),( 'OX1 1EX' ),( 'OX1 1GA' ),( 'OX1 1GB' ),( 'OX1 1GD' ),( 'OX1 1GE' ),( 'OX1 1GF' ),
    ( 'OX1 1GH' ),( 'OX1 1GJ' ),( 'OX1 1GL' ),( 'OX1 1HB' ),( 'OX1 1HD' ),( 'OX1 1HF' ),( 'OX1 1HG' ),( 'OX1 1HH' ),( 'OX1 1HN' ),( 'OX1 1HP' ),
    ( 'OX1 1HQ' ),( 'OX1 1HR' ),( 'OX1 1HS' ),( 'OX1 1HT' ),( 'OX1 1HU' ),( 'OX1 1HW' ),( 'OX1 1HX' ),( 'OX1 1HY' ),( 'OX1 1HZ' ),( 'OX1 1JA' ),
    ( 'OX1 1JB' ),( 'OX1 1JD' ),( 'OX1 1JE' ),( 'OX1 1JF' ),( 'OX1 1JG' ),( 'OX1 1JH' ),( 'OX1 1JJ' ),( 'OX1 1JL' ),( 'OX1 1JP' ),( 'OX1 1JQ' ),
    ( 'OX1 1JR' ),( 'OX1 1JS' ),( 'OX1 1JT' ),( 'OX1 1JU' ),( 'OX1 1JW' ),( 'OX1 1JX' ),( 'OX1 1JY' ),( 'OX1 1JZ' ),( 'OX1 1LB' ),( 'OX1 1LD' ),
    ( 'OX1 1LE' ),( 'OX1 1LF' ),( 'OX1 1LG' ),( 'OX1 1LJ' ),( 'OX1 1LL' ),( 'OX1 1LQ' ),( 'OX1 1LT' ),( 'OX1 1LU' ),( 'OX1 1LY' ),( 'OX1 1ND' )
GO

SELECT * FROM dbo.postCodes
SELECT * FROM dbo.postCodeParts ORDER BY xStart, xLen

SELECT * 
FROM dbo.postCodes pc
    INNER JOIN dbo.postCodeParts pcp ON pc.postcodeId = pcp.postcodeId
WHERE postcodePart = '1J'
ORDER BY xStart, xLen
GO

IF OBJECT_ID('dbo.usp_searchPostCodes') IS NOT NULL DROP PROC dbo.usp_searchPostCodes
GO
CREATE PROC dbo.usp_searchPostCodes

    @searchString   VARCHAR(8)

AS

    SET NOCOUNT ON

    --!!TODO add error handling
    --!!TODO does not deal with middle wildcards or _ wildcard

    DECLARE @leadingWildCard BIT
    DECLARE @cleanSearchString VARCHAR(8)

    SELECT @leadingWildCard = CASE WHEN LEFT( @searchString, 1 ) = '%' THEN 1 ELSE 0 END
    SELECT @cleanSearchString = REPLACE( REPLACE( @searchString, ' ', '' ), '%', '' )

    -- Debugging
    --PRINT @leadingWildCard
    --PRINT @cleanSearchString

    IF @leadingWildCard = 0

        -- No leading wildcard, start at position 1
        SELECT pc.postcode
        FROM dbo.postCodes pc
            INNER JOIN dbo.postCodeParts pcp ON pc.postcodeId = pcp.postcodeId
        WHERE pcp.postcodePart = @cleanSearchString
          AND pcp.xstart = 1
        ORDER BY xStart, xLen

    ELSE

        -- Leading wildcard, return all positions
        SELECT pc.postcode
        FROM dbo.postCodes pc
            INNER JOIN dbo.postCodeParts pcp ON pc.postcodeId = pcp.postcodeId
        WHERE pcp.postcodePart = @cleanSearchString
        ORDER BY xStart, xLen

RETURN
GO


EXEC dbo.usp_searchPostCodes 'OX1 1J%'
EXEC dbo.usp_searchPostCodes '%X1 1J%'
GO


SELECT xStart, xLen, postcodePart
FROM dbo.postCodes pc
    INNER JOIN dbo.postCodeParts pcp ON pc.postcodeId = pcp.postcodeId
WHERE pc.postcode= 'OX1 1JZ'
ORDER BY xStart, xLen

在100万行表上创建LIKE查询的聚簇索引或非聚簇索引？

1 个答案: