Oracle's listagg () WITHIN GROUP () function

https: // www.cnblogs.com/sjxbg/p/9859100.html I 

wrote a similar statement in 2018 but I have no impression at all: 

listagg (cloumn, ' conconate marker ' ) within group (order by column)

1. Use conditional query Query the list of employees with department 20

    -Query the list of employees with department 20
    SELECT t.DEPTNO, t.ENAME FROM SCOTT.EMP t where t.DEPTNO = '20';

    Effect:

2. Use listagg () WITHIN GROUP () to merge multiple lines into one line

    SELECT
       T .DEPTNO,
       listagg (T .ENAME, ',') WITHIN GROUP (ORDER BY T .ENAME) names
    FROM
       SCOTT.EMP T
    WHERE
       T .DEPTNO = '20'
    GROUP BY
       T .DEPTNO

    effect:

3. Use listagg () within GROUP () over to record multiple rows on one line.

    SELECT
       T .DEPTNO,
       listagg (T .ENAME, ',') WITHIN GROUP (ORDER BY T .ENAME) over (PARTITION BY T .DEPTNO)
    FROM
       SCOTT.EMP T
    WHERE
       T .DEPTNO = '20'

    effect:

Note: The table data used is the emp (employee) table under the oracle user scott

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When you have two columns A and B in table X, the data is as follows

A　　B

a　　1

a　　2

a　　3

b　　1

b　　2

b　　3

To display data in a | 1 | 2 | 3, b | 1 | 2 | 3 format, use listagg ()

1. Use listagg () + group by

select A,B,listagg(B,'|') within GROUP (order by A) C from X group by A;

over (partition by class order by sroce) Accumulate according to sroce sorting, order by is a default windowing function, and partition by class.

2、使用listagg() + over(partition by ?)

select A,B listagg(B,'|') within Group(order by A) over(partition by A) C from X;

DBMS_LOB.SUBSTR (col1) does not pass other parameters is to read all

DBMS_LOB.SUBSTR (col1,10,1) means take 10 bytes from the first byte

DBMS_LOB.SUBSTR (CLOB_VAR, 32767) means to intercept all data saved by CLOB variables

DBMS_LOB.FILECLOSE (IMG_BFILE) close the file

People are timid and run with big swords in their hands.