Oracle DECODE 和 CASE 用法

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Oracle DECODE & CASE Functions

Version 11.1

Note:Decode and Case are very similar in their appearance but can produce very different results.

Demo Tables & Data

Airplanes Table

Locations Table

All other tables

DECODE (overload 1)

standard.DECODE(exprNUMBER,patNUMBER,resNUMBER)RETURN NUMBER;

DECODE (overload 2)

standard.DECODE(
exprNUMBER,
patNUMBER,
resVARCHAR2CHaraCTER SET ANY_CS)
returnVARCHAR2CHaraCTER SET res%CHARSET;

DECODE (overload 3)

standard.DECODE(exprNUMBER,resDATE)RETURN DATE;

DECODE (overload 4)

standard.DECODE(
exprVARCHAR2CHaraCTER SET ANY_CS,
patVARCHAR2CHaraCTER SET expr%CHARSET,
resNUMBER)
RETURNNUMBER;

DECODE (overload 5)

standard.DECODE(
exprVARCHAR2CHaraCTER SET ANY_CS,
resVARCHAR2CHaraCTER SET ANY_CS)
RETURNVARCHAR2CHaraCTER SET res%CHARSET;

DECODE (overload 6)

standard.DECODE(
exprVARCHAR2CHaraCTER SET ANY_CS,
resDATE)
RETURNDATE;

DECODE (overload 7)

standard.DECODE(exprDATE,patDATE,resNUMBER)RETURN NUMBER;

DECODE (overload 8)

standard.DECODE(
exprDATE,
patDATE,
resVARCHAR2CHaraCTER SET ANY_CS)
RETURNVARCHAR2CHaraCTER SET res%CHARSET;

DECODE (overload 9)

standard.DECODE( exprDATE,patDATE,resDATE)RETURN DATE;

DECODE (overload 10)

standard.DECODE(exprOBJECT,patOBJECT,resOBJECT)RETURNOBJECT;

DECODE (overload 11)

standard.DECODE(exprUNDEFINED,patUNDEFINED,resUNDEFINED)
RETURNUNDEFINED;

Decode Built-in Function

Simple DECODE

SELECT DECODE(value,<if this value>,<return this value>)
FROM DUAL;

SELECTprogram_id,
DECODE(customer_id,'AAL','American Airlines') AIRLINE,
delivered_date
FROMairplanes
WHERE ROWNUM< 11;

More Complex DECODE

SELECT DECODE(value,<if this value>,<return this value>,
<if this value>,<return this value>,
....)
FROM DUAL;

SELECTprogram_id,
DECODE(customer_id,
'AAL','American Airlines',
'ILC','Intl. Leasing Corp.',
'NWO','northwest Orient',
'SAL','Southwest Airlines',
'SWA','Sweptwing Airlines',
'USAF','U.S. Air Force') AIRLINE,
delivered_date
FROMairplanes
WHERE ROWNUM< 11;

DECODE with DEFAULT

SELECT DECODE(value,<return this value>,
<if this value>,
....
<otherwise this value>)
FROM DUAL;

SELECTprogram_id,
'AAL','American Airlines',
'ILC','Intl. Leasing Corp.',
'NWO','northwest Orient',
'SAL','Southwest Airlines',
'SWA','Sweptwing Airlines',
'USAF','United States Air Force',
'Not KNown') AIRLINE,
delivered_date
FROMairplanes
WHERE ROWNUM< 11;

Note:The following crosstabulation is the standard for 10g or earlier. In 11g use the PIVOT and UNPIVOT operators

Simple DECODE Crosstab

Note how each decode only looks at a single possible value and turns it into a new column

SELECTprogram_id,
DECODE(customer_id,'AAL')AMERICAN,'DAL','DAL')DELTA,'NWO','NWO')norTHWEST,'ILC','ILC')INTL_LEASING
FROMairplanes
WHERE ROWNUM< 20;

DECODE as an in-line view with crosstab summation

The above DECODE,in blue,used as an in-line view

SELECTprogram_id,
COUNT(AMERICAN) AAL,
COUNT(DELTA) DAL,
COUNT(norTHWEST) NWO,
COUNT(INTL_LEASING) ILC
FROM(
SELECTprogram_id,'ILC')INTL_LEASING
FROMairplanes)
GROUP BYprogram_id;

Query for DECODE demo

CREATE TABLEstores (
store_name VARCHAR2(20),
region_dir NUMBER(5),
region_mgrNUMBER(5),
store_mgr1NUMBER(5),
store_mgr2NUMBER(5),
asst_storemgr1NUMBER(5),
asst_storemgr2NUMBER(5),
asst_storemgr3NUMBER(5));

INSERT INTOstores
VALUES('San Francisco',100,200,301,302,401,403);

INSERT INTOstores
VALUES('Oakland',404,0);

INSERT INTOstores
VALUES('Palo Alto',305,405,406);

INSERT INTOstores
VALUES('Santa Clara',250,306,407);
COMMIT;

SELECTDECODE(asst_storemgr1,
DECODE(asst_storemgr2,
DECODE(asst_storemgr3,asst_storemgr3),
asst_storemgr2),asst_storemgr1)Asst_MANAGER,
DECODE(store_mgr1,DECODE(store_mgr2,store_mgr2),
store_mgr1)STORE_MANAGER,
REGION_MGR,
REGION_DIR
FROMstores;

DECODE with Summary Function

SELECT SUM(CA_COUNT) CA,SUM(TX_COUNT) TX
FROM(
SELECTstate,
DECODE(state,'CA',COUNT(*),0) CA_COUNT,'TX',0) TX_COUNT
FROMlocations
GROUP BYstate);

DECODE in theWHEREclause

set serveroutput on

DECLARE
posnPLS_INTEGER:= 0;
empidPLS_INTEGER:= 178;
xNUMBER;
BEGIN
SELECT NVL(SUM(ah.quantity * ah.saleprice * ap.payoutpct),0)
INTOx
FROMaccessoryhistory ah,payoutpercentage ap,
sku s,store st
WHEREempid =DECODE(posn,
0,st.areadir,
1,st.areamgr,
2,NVL(st.storemgr1,st.storemgr2),
3,NVL(st.asstmgr1,NVL(st.asstmgr2,
st.asstmgr3)))
ANDah.statustypeIN('ACT','DEA')
ANDah.store = st.store
ANDs.dbid = ah.dbid
ANDs.sku = ah.sku
ANDap.productgroup = s.productgroup
ANDap.position = posn;

dbms_output.put_line(x);
END;
/

DECODE Altered WHERE Clause

Thanks to HJL

CREATE TABLEtest (
pubdateDATE,
compdateDATE,
valuecolNUMBER(5));

INSERT INTOtestVALUES(TRUNC(SYSDATE),TRUNC(SYSDATE+300),1);
INSERT INTOtestVALUES(TRUNC(SYSDATE-300),TRUNC(SYSDATE),9);
COMMIT;

SELECT*FROMtest;

CREATEORREPLACE PROCEDUREtestproc (
StartDateDATE,EndDateDATE,DateTypeIN VARCHAR2) IS

iPLS_INTEGER;
BEGIN
SELECTvaluecol
INTOi
FROMtest
WHERE DECODE(DateType,'AA',compdate,'BB',pubdate,compdate) <= EndDate
AND DECODE(DateType,compdate) >= StartDate;

dbms_output.put_line(TO_CHAR(i));
ENDtestproc;
/

set serveroutput on

exec testproc(TRUNC(SYSDATE),'BB');

CASE

Simple CASE Demo

SELECT CASE WHEN(<column_value>=<value>)THEN
WHEN(<column_value>=<value>)THEN
ELSE<value>
FROM<table_name>;

SELECTline_number,
CASE WHEN(line_number = 1)THEN'One'
WHEN(line_number = 2)THEN'Two'
ELSE'More Than Two'
ENDASRESULTSET
FROMairplanes;

More Complex CASE Demo With Between

SELECT CASE WHEN(<column_value>BETWEEN<value>
AND<value>)THEN
WHEN(<column_value>
BETWEEN<value>AND<value>)THEN
ELSE<value>
FROM<table_name>;

SELECTline_number,
CASE WHEN(line_numberBETWEEN1AND10)THEN'One'
WHEN(line_numberBETWEEN11AND100)THEN'Big'
ELSE'Bigger'
END
FROMairplanes;

More Complex CASE Demo With Booleans

SELECT CASE WHEN(<column_value><=<value>)THEN
WHEN(<column_value><=<value>)THEN
ELSE<value>
FROM<table_name>;

SELECTline_number,
CASEWHEN(line_number < 10)THEN'Ones'
WHEN(line_number < 100)THEN'Tens'
WHEN(line_number < 1000)THEN'Hundreds'
ELSE'Thousands'
ENDRESULT_SET
FROMairplanes;

The above demo turned into a view

CREATEORREPLACEVIEW line_number_view AS
SELECTline_number,
CASE WHEN(line_number < 10)THEN'Ones'
WHEN(line_number < 100)THEN'Tens'
WHEN(line_number < 1000)THEN'Hundreds'
ELSE'Thousands'
ENDRESULT_SET
FROMairplanes;

CASE with BOOLEANS

set serveroutput on

DECLARE
boolvarBOOLEAN:=TRUE;
BEGIN
dbms_output.put_line(CASEboolvarWHEN TRUE THEN'TRUE'WHEN FALSE THEN
'FALSE'END);
END;
/

CASE - DECODE Comparison

The same functionality written using both functions

SELECTparameter,DECODE(SIGN(parameter-1000),-1,'C','P')ASBAND
FROMparameter_table;

SELECTparameter,
CASE WHENparameter < 1000THEN'C'ELSE'P'END ASBAND
FROMparameter_table;

Another example using SIGN

SELECTmin_cached,COUNT(*),ROUND(AVG(executions),2)
FROM(
SELECT DECODE(min_cached,'1) 00-01 min',
1,'2) 01-02min',
2,
DECODE(SIGN(min_cached -6),'3) 03-05min',
DECODE(SIGN(min_cached -16),'4) 06-15min',
DECODE(SIGN(min_cached -31),'5) 16-30min',
DECODE(SIGN(min_cached -61),'6) 31-60min',
DECODE(SIGN(min_cached-121),'7) 1-2hrs',
'8) 2 hrs+ ')))))) min_cached,
executions
FROM(
SELECT ROUND((SYSDATE-
TO_DATE(first_load_time,'YYYY-MM-DD/HH24:MI:SS'))*24*60) min_cached,
executions
FROMgv$sqlarea
WHEREparsing_user_id != 0)
)
GROUP BYmin_cached

Oracle DECODE 和 CASE 用法

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