一个字段可以本身即有单独索引也属于某联合索引之一吗？

IF EXISTS (SELECT 1

            FROM  SYSINDEXES

           WHERE  ID    = OBJECT_ID('TABLE_1')

            AND   NAME  = 'INDEX_3'

            AND   INDID > 0

            AND   INDID < 255)

   DROP INDEX TABLE_1.INDEX_3

go



IF EXISTS (SELECT 1

            FROM  SYSINDEXES

           WHERE  ID    = OBJECT_ID('TABLE_1')

            AND   NAME  = 'INDEX_2'

            AND   INDID > 0

            AND   INDID < 255)

   DROP INDEX TABLE_1.INDEX_2

go



IF EXISTS (SELECT 1

            FROM  SYSOBJECTS

           WHERE  ID = OBJECT_ID('TABLE_1')

            AND   TYPE = 'U')

   DROP TABLE TABLE_1

go



/*==============================================================*/

/* Table: TABLE_1                                               */

/*==============================================================*/

CREATE TABLE TABLE_1 (

   COLUMN_1             INT                  NOT NULL,

   COLUMN_2             INT                  NOT NULL,

   COLUMN_3             INT                  NOT NULL,

   CONSTRAINT PK_TABLE_1 PRIMARY KEY (COLUMN_1)

)

go



/*==============================================================*/

/* Index: INDEX_2                                               */

/*==============================================================*/

CREATE INDEX INDEX_2 ON TABLE_1 (

COLUMN_1 ASC,

COLUMN_2 ASC,

COLUMN_3 ASC

)

go



/*==============================================================*/

/* Index: INDEX_3                                               */

/*==============================================================*/

CREATE INDEX INDEX_3 ON TABLE_1 (

COLUMN_1 ASC,

COLUMN_2 ASC

)

go