Help Center/ GaussDB(DWS)/ Tool Guide/ DSC/ Oracle Syntax Migration/ Schema Objects/ Indexes
Updated on 2024-07-19 GMT+08:00
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Indexes

When an index is created in GaussDB(DWS), a schema name cannot be specified along with the index name. The index will be automatically created in the schema where the index table is created.

Figure 1 Input: INDEX
Figure 2 Output: INDEX

Input - Function-based indexes by using CASE

A function-based index is an index that is created on the results of a function or expression on top of a column.

Output

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CREATE
     UNIQUE index GCC_RSRC_ASSIGN_U1
          ON GCC_PLAN.GCC_RSRC_ASSIGN_T (
          (CASE
               WHEN( ENABLE_FLAG = 'Y' AND ASSIGN_TYPE = '13' AND WORK_ORDER_ID IS NOT NULL )
               THEN WORK_ORDER_ID
               ELSE NULL
          END)
     ) ;

The expression or function needs to be put inside brackets.

Input - Function-based indexes by using DECODE

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CREATE UNIQUE index GCC_PLAN_N2
          ON GCC_PLAN.GCC_PLAN_T (
          DECODE (
               ENABLE_FLAG
               ,'Y'
               ,BUSINESS_ID
               ,NULL
          )
     ) ;

Output

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CREATE UNIQUE index GCC_PLAN_N2
          ON GCC_PLAN.GCC_PLAN_T (
          (DECODE (
               ENABLE_FLAG
               ,'Y'
               ,BUSINESS_ID
               ,NULL
          ))
     ) ;

The expression or function needs to be put inside brackets.

ORA_HASH

ORA_HASH is a function that computes a hash value for a given expression or column. If this function is specified on the column(s) in the CREATE INDEX statement, this function will be removed.

Input

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CREATE INDEX SD_WO.WO_WORK_ORDER_T_N3 on SD_WO.WO_WORK_ORDER_T (PROJECT_NUMBER, ORA_HASH(WORK_ORDER_NAME));

Output

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CREATE
index WO_WORK_ORDER_T_N3
ON SD_WO.WO_WORK_ORDER_T (
PROJECT_NUMBER
,ORA_HASH( WORK_ORDER_NAME )
) ;

DECODE

If DECODE function in the CREATE INDEX statement is used as a part of a column, the following error will be reported: "syntax error at or near 'DECODE' (Script - gcc_plan_t.sql)".

Input

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CREATE UNIQUE index GCC_PLAN.GCC_PLAN_N2 on GCC_PLAN.GCC_PLAN_T (DECODE(ENABLE_FLAG,'Y',BUSINESS_ID,NULL));

Output

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CREATE
UNIQUE index GCC_PLAN_N2
ON GCC_PLAN.GCC_PLAN_T (
DECODE (
ENABLE_FLAG
,'Y'
,BUSINESS_ID
,NULL
)
) ;

CASE statement

The CASE statement is not supported in the CREATE INDEX statement.

Input

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CREATE
     UNIQUE index GCC_RSRC_ASSIGN_U1
          ON GCC_PLAN.GCC_RSRC_ASSIGN_T (
          (CASE
               WHEN( ENABLE_FLAG = 'Y' AND ASSIGN_TYPE = '13' AND WORK_ORDER_ID IS NOT NULL )
               THEN WORK_ORDER_ID
               ELSE NULL
          END)
     ) ;

Output

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CREATE UNIQUE INDEX gcc_rsrc_assign_u1 
  ON gcc_plan.gcc_rsrc_assign_t ( (( CASE 
                                                        WHEN( enable_flag = 'Y' 
                                                                  AND assign_type = '13' 
                                                                  AND work_order_id IS NOT NULL ) 
                                                  THEN work_order_id 
                                                  ELSE NULL END )) );
Parent topic: Schema Objects