Oracle's SUBSTR function

First, substr function

SUBSTR (target string, start position, length)

Note: Here the third parameter: length, equivalent to the scalar in physics, there is no directionality, so you cannot use negative values. Although no error, but choose No value out ( please correct )

The start position can have a negative value, indicating the reciprocal. For example: substr (ename,-2,2): Indicates that a string of length 2 is truncated from the first countdown

Example 1:

Sql> Select Ename,substr (ename,1,3) from EMP;

Ename SUBSTR
---------- 　　 ------
SMITH SMI
ALLEN All
WARD WAR
JONES JON
MARTIN MAR
BLAKE BLA
CLARK CLA
SCOTT SCO
KING KIN
TURNER TUR
ADAMS ADA
JAMES JAM
FORD for
MILLER MIL

14 rows have been selected.

Example 2:

Sql> Select Ename,substr (ename,-2,2) from EMP;

Ename SUBS
---------- ----
SMITH TH
ALLEN EN
WARD RD
JONES ES
MARTIN in
BLAKE KE
CLARK RK
SCOTT TT
KING NG
TURNER ER
ADAMS MS
JAMES ES
FORD RD
MILLER ER

14 rows have been selected.

Example 3:

Sql> Select Ename,substr (ename,2,-2) from EMP;

Ename S
---------- -
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER
Adams
JAMES
FORD
MILLER

14 rows have been selected.

Oracle's SUBSTR function