本文分享自华为云社区《GaussDB(DWS)性能调优：典型不下推语句整改案例》，作者： 譡里个檔 。

场景1：With-Recursive contains only values rte is not shippable

根因：递归语句的某个分支中没有FROM字句（只有 VALUES 或者类似 SELECT 1 这样的语句）

案例1：递归驱动分支没有FROM字句

原始语句

【资料图】

SELECT T.RPT_ITEM_ID, --报表项IDT.RPT_ITEM_CODE,T.USER_GROUP_CODE AS USER_GROUP_CODE --用户组FROM BIF.BIF_RPT_ITEM_DEF_T T,(WITH recursive cte AS (SELECT DISTINCT TRIM(SUBSTR("" :: text, INSTR("", ",", 1, 1) + 1, INSTR("", ",", 1, 2) - INSTR("", ",", 1, 1) - 1)) AS cte_RPT_ITEM_CODE,1 AS levelFROM (SELECT "") AS tb0UNION ALLSELECT DISTINCT TRIM(SUBSTR("" :: text, INSTR("", ",", 1, cte.level + 1) + 1, INSTR("", ",", 1, cte.level + 2) - INSTR("", ",", 1, cte.level + 1) - 1)),cte.level + 1FROM (SELECT "") AS tb0, cteWHERE cte.level + 1 <= LENGTH("") - LENGTH(REPLACE("", ",", "")) - 1)SELECTDISTINCT cte_RPT_ITEM_CODE AS RPT_ITEM_CODEFROM cte) T5WHERE NVL(INSTR(T.RPT_ITEM_FREQUENCE, "M"), 0) > 0AND T.RPT_ITEM_CODE = NVL(T5.RPT_ITEM_CODE, T.RPT_ITEM_CODE)AND T.RPT_ITEM_TYPE = 1 --是否是叶子报表项，1=是，0=否，基本报表项AND T.ENABLE_FLAG = 1AND T.VERSION = "202308" --使用快照,增加条件限制ORDER BY T.RPT_ITEM_ID

改写语句

SELECT T.RPT_ITEM_ID, --报表项IDT.RPT_ITEM_CODE,T.USER_GROUP_CODE AS USER_GROUP_CODE --用户组FROM BIF.BIF_RPT_ITEM_DEF_T T,(WITH recursive cte AS (SELECT DISTINCT TRIM(SUBSTR("" :: text, INSTR("", ",", 1, 1) + 1, INSTR("", ",", 1, 2) - INSTR("", ",", 1, 1) - 1)) AS cte_RPT_ITEM_CODE,1 AS levelFROM (SELECT "") AS tb0UNION ALLSELECT DISTINCT TRIM(SUBSTR("" :: text, INSTR("", ",", 1, cte.level + 1) + 1, INSTR("", ",", 1, cte.level + 2) - INSTR("", ",", 1, cte.level + 1) - 1)),cte.level + 1FROM (SELECT "") AS tb0, cteWHERE cte.level + 1 <= LENGTH("") - LENGTH(REPLACE("", ",", "")) - 1)SELECTDISTINCT cte_RPT_ITEM_CODE AS RPT_ITEM_CODEFROM cte) T5WHERE NVL(INSTR(T.RPT_ITEM_FREQUENCE, "M"), 0) > 0AND T.RPT_ITEM_CODE = NVL(T5.RPT_ITEM_CODE, T.RPT_ITEM_CODE)AND T.RPT_ITEM_TYPE = 1 --是否是叶子报表项，1=是，0=否，基本报表项AND T.ENABLE_FLAG = 1AND T.VERSION = "202308" --使用快照,增加条件限制ORDER BY T.RPT_ITEM_ID

修改点比对

案例2：递归驱动分支没有FROM字句

原始语句

SELECT A.DYNM_COMP_ID,DECODE(B.LINE_NO, 1, "202308", A.VERSION)FROM BIF.BIF_DYNM_COMP_SOU_TBL_V A,(WITH recursive cte AS (SELECT 1 AS levelUNION ALLSELECT cte.level + 1FROM cteWHERE cte.level + 1 < 3)SELECTlevel as LINE_NOFROM cte) BWHERE EXISTS (SELECT 1FROM BIF.BIF_RPT_ITEM_DEF_MV RPT,BIF.BIF_PUB_SUBJECT_AREA_T SBJ,BIF.BIF_SNAPSHORT_SUBJECT_V TYPWHERE A.DYNM_COMP_ID = RPT.DYNM_COMP_IDAND RPT.VERSION = "current"AND RPT.SUBJECT_AREA_ID = SBJ.SUBJECT_AREA_IDAND SBJ.SUBJECT_AREA_CODE =TYP.SUBJECT_CODEAND TYP.SUBJECT_TYPE ="TAX")AND A.VERSION = "current"

改写语句

SELECT A.DYNM_COMP_ID,DECODE(B.LINE_NO, 1, "202308", A.VERSION)FROM BIF.BIF_DYNM_COMP_SOU_TBL_V A,(SELECT*FROM generate_series(1, 2) AS cte(LINE_NO)) BWHERE EXISTS (SELECT 1FROM BIF.BIF_RPT_ITEM_DEF_MV RPT,BIF.BIF_PUB_SUBJECT_AREA_T SBJ,BIF.BIF_SNAPSHORT_SUBJECT_V TYPWHERE A.DYNM_COMP_ID = RPT.DYNM_COMP_IDAND RPT.VERSION = "current"AND RPT.SUBJECT_AREA_ID = SBJ.SUBJECT_AREA_IDAND SBJ.SUBJECT_AREA_CODE =TYP.SUBJECT_CODEAND TYP.SUBJECT_TYPE ="TAX")AND A.VERSION = "current"

修改点比对

案例3：递归驱动分支是VALUES字句

原始语句

WITH RECURSIVE t(n) AS (VALUES (1)UNION ALLSELECTn+1FROM tWHERE n < (SELECT MAX(LENGTH(COMP_CODE)-LENGTH(REPLACE(COMP_CODE,",","")))+1 MAX_TOKENSFROM (SELECT DEPT_CODE,to_char(APPLICABLE_GEO_PC_CODE) COMP_CODEFROM SDIHR.MDM_CDM_DEPT_ACT_INFO_T_3600)))SELECT n AS LVL FROM t

改写语句

WITH RECURSIVE t(n) AS (SELECT * FROM generate_series(1, 1)UNION ALLSELECTn+1FROM tWHERE n < (SELECT MAX(LENGTH(COMP_CODE)-LENGTH(REPLACE(COMP_CODE,",","")))+1 MAX_TOKENSFROM (SELECT DEPT_CODE,to_char(APPLICABLE_GEO_PC_CODE) COMP_CODEFROM SDIHR.MDM_CDM_DEPT_ACT_INFO_T_3600)))SELECT n AS LVL FROM t

修改点比对

案例4：递归驱动分支是VALUES字句

原始语句

WITH RECURSIVE t(n) AS (VALUES (1)UNION ALLSELECTn+1FROM tWHERE n < (SELECT MAX(LENGTH(COMP_CODE)-LENGTH(REPLACE(COMP_CODE,",","")))+1 MAX_TOKENSFROM (SELECT DEPT_CODE,to_char(APPLICABLE_GEO_PC_CODE) COMP_CODEFROM SDIHR.MDM_CDM_DEPT_ACT_INFO_T_3600)))SELECT n AS LVL FROM t

改写语句

SELECT*FROM generate_series(1, (SELECT MAX(LENGTH(COMP_CODE)-LENGTH(REPLACE(COMP_CODE,",","")))+1 MAX_TOKENSFROM (SELECT DEPT_CODE,to_char(APPLICABLE_GEO_PC_CODE) COMP_CODEFROM SDIHR.MDM_CDM_DEPT_ACT_INFO_T_3600))) AS t(lvl)

修改点比对

场景2：With-Recursive contains system table is not shippable

根因：递归语句的某个分支中没有FROM字句中只用系统表或者系统视图(DUAL也被视为系统视图)

案例1：递归驱动分支是FROM DUAL查询

原始语句

WITH recursive cte AS (SELECTTO_DATE(201701, "YYYYMM") as level ,TO_DATE(20170131, "YYYYMMDD") LASTDAYFROM dualUNION ALLSELECTADD_MONTHS(cte.LEVEL, 1) AS PERIOD,LAST_DAY(ADD_MONTHS(cte.LEVEL, 1)) AS LASTDAYFROM cte WHERE cte.LEVEL <=SYSDATE)SELECTTO_CHAR(cte.level,"YYYYMMDD") AS PERIOD , cte.LASTDAYFROM cteWHERE TO_CHAR(cte.level,"YYYYMMDD")<= TO_CHAR(SYSDATE,"YYYYMMDD")

改写语句

WITH recursive cte AS (SELECTTO_DATE(201701, "YYYYMM") as level ,TO_DATE(20170131, "YYYYMMDD") LASTDAYFROM dualUNION ALLSELECTADD_MONTHS(cte.LEVEL, 1) AS PERIOD,LAST_DAY(ADD_MONTHS(cte.LEVEL, 1)) AS LASTDAYFROM cte WHERE cte.LEVEL <=SYSDATE)SELECTTO_CHAR(cte.level,"YYYYMMDD") AS PERIOD , cte.LASTDAYFROM cteWHERE TO_CHAR(cte.level,"YYYYMMDD")<= TO_CHAR(SYSDATE,"YYYYMMDD")

修改点对比

场景3：SubPlan exec on CN can"t be shipped

根因：某个子查询语句只能在CN上执行，通常是这个子查询有不下推因素，比如有系统表、系统视图调用，或者存在不下推函数等

案例1：子查询中系统表/系统视图查询

原始语句

WITH error_log AS NOT MATERIALIZED (SELECTupper(log_column_name) AS log_column_name,log_error_code,s.char_length AS data_length,s.data_type,s.nullableFROM (SELECTdistinctunnest(string_to_array(bad_log_column_name,",")) AS log_column_name,unnest(string_to_array(bad_log_error_code,",")) AS log_error_codeFROM stgltc.BAD_cfs_inv_invoice_ad_2500) T,(SELECT * FROM user_tab_columns WHERE table_name=lower("dlt_cfs_inv_invoice_ad_2500")) SWHERE upper(T.log_column_name)=upper(S.column_name))SELECTCASE WHEN upper("ACTIVITY_NAME") IN (SELECT log_column_name FROM error_log WHERE data_type IN ("varchar","char","character","nchar","character varying","varchar2","nvarchar2","clob","text") AND log_error_code="22001"/*字符超长*/)THEN SUBSTRB(ACTIVITY_NAME,0,(SELECT distinct DATA_LENGTH FROM error_log WHERE upper(log_column_name)=upper("ACTIVITY_NAME")))ELSE ACTIVITY_NAMEEND AS ACTIVITY_NAME,CASE WHEN upper("ADJUSTMENT_ID") IN (SELECT log_column_name FROM error_log WHERE data_type IN ("varchar","char","character","nchar","character varying","varchar2","nvarchar2","clob","text") AND log_error_code="22001"/*字符超长*/)THEN SUBSTRB(ADJUSTMENT_ID,0,(SELECT distinct DATA_LENGTH FROM error_log WHERE upper(log_column_name)=upper("ADJUSTMENT_ID")))ELSE ADJUSTMENT_IDEND AS ADJUSTMENT_IDFROM stgltc.BAD_cfs_inv_invoice_ad_2500

改写语句

-- 识别不下推的子查询为WITH error_log字句中的-- SELECT * FROM user_tab_columns WHERE table_name=lower("dlt_cfs_inv_invoice_ad_2500")---- 因为这部分为系统表查询，无论如何都不能下推，所以此处把这部分结果转储到一个中间表中-- 中间表创建成行存表CREATE TEMP TABLE s WITH(orientation=row) DISTRIBUTE BY ROUNDROBIN ASSELECT * FROM user_tab_columns WHERE table_name=lower("dlt_cfs_inv_invoice_ad_2500")-- 因为整个查询涉及到的表都是列存表，之后前面创建的临时表s为行存表-- 所以此处加一个强制走向量化的hintWITH error_log AS NOT MATERIALIZED (SELECTupper(log_column_name) AS log_column_name,log_error_code,s.char_length AS data_length,s.data_type,s.nullableFROM (SELECTdistinctunnest(string_to_array(bad_log_column_name,",")) AS log_column_name,unnest(string_to_array(bad_log_error_code,",")) AS log_error_codeFROM stgltc.bad_cfs_inv_invoice_ad_2500) T,pg_temp.SWHERE upper(T.log_column_name)=upper(S.column_name))SELECT /*+ set global(enable_force_vector_engine on)*/CASE WHEN upper("ACTIVITY_NAME") IN (SELECT log_column_name FROM error_log WHERE data_type IN ("varchar","char","character","nchar","character varying","varchar2","nvarchar2","clob","text") AND log_error_code="22001"/*字符超长*/)THEN SUBSTRB(ACTIVITY_NAME,0,(SELECT distinct DATA_LENGTH FROM error_log WHERE upper(log_column_name)=upper("ACTIVITY_NAME")))ELSE ACTIVITY_NAMEEND AS ACTIVITY_NAME,CASE WHEN upper("ADJUSTMENT_ID") IN (SELECT log_column_name FROM error_log WHERE data_type IN ("varchar","char","character","nchar","character varying","varchar2","nvarchar2","clob","text") AND log_error_code="22001"/*字符超长*/)THEN SUBSTRB(ADJUSTMENT_ID,0,(SELECT distinct DATA_LENGTH FROM error_log WHERE upper(log_column_name)=upper("ADJUSTMENT_ID")))ELSE ADJUSTMENT_IDEND AS ADJUSTMENT_IDFROM stgltc.bad_cfs_inv_invoice_ad_2500

修改点对比

场景4：Type of Record in TargetList can not be shipped

根因：输出列中存在record类型，这种类型的不下推一般是不会体现在最外层的输出列上，一般这类报错有两个场景

1.SQL书写逻辑错误，导致输出列上出现了（...）形式的输出列

2.SQL业务逻辑正确， 这种场景需要了解业务含义，把record字段强转为text类型，然后再使用record字段的地方做特殊适配

案例1：输出列书写错误，出现（...）形式的输出列

原始语句

SELECTd.id,coalesce(d.period, "snull") AS period,(d.plan_unit_code, "snull") AS plan_unit_code,coalesce(d.product_type_model, "snull") AS product_type_model,coalesce(d.revision, "snull") AS revision,d.start_dateFROM (SELECT *FROM cdcscm.cdc_mp_d_forecast_t_6120 tWHERE t.cdc_timestamp > to_date("2023-07-06 00:00:00", "yyyy-mm-dd hh24:mi:ss") - 7AND t.cdc_timestamp < to_date("2023-08-08 00:00:00", "yyyy-mm-dd hh24:mi:ss")) t1,sdiscm.mp_d_forecast_t_6120 dWHERE (t1.audit_op_type = "delete" AND t1.audit_op_option = "before")AND d.id = t1.id

改写语句

SELECTd.id,coalesce(d.period, "snull") AS period,coalesce(d.plan_unit_code, "snull") AS plan_unit_code,coalesce(d.product_type_model, "snull") AS product_type_model,coalesce(d.revision, "snull") AS revision,d.start_dateFROM (SELECT *FROM cdcscm.cdc_mp_d_forecast_t_6120 tWHERE t.cdc_timestamp > to_date("2023-07-06 00:00:00", "yyyy-mm-dd hh24:mi:ss") - 7AND t.cdc_timestamp < to_date("2023-08-08 00:00:00", "yyyy-mm-dd hh24:mi:ss")) t1,sdiscm.mp_d_forecast_t_6120 dWHERE (t1.audit_op_type = "delete" AND t1.audit_op_option = "before")AND d.id = t1.id

修改点对比

备注：改写前后语句不等价，不等价的原因是因为原始SQL书写有问题，正确的写法是就是coalesce(d.plan_unit_code, "snull") AS plan_unit_code。

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