Postgres Type Conversion Cast

Transferred from: http://blog.csdn.net/yufenghyc/article/details/45869509

--1 Example
postgres=# Select 1/4;
? column?
----------
0
(1 row)

In PG If you want to do division and want to keep decimals, the method above does not work, because the "/" Operation results are rounded, and the fractional part is truncated.

--2 Type Conversions
postgres=# Select round (1:: Numeric/4:: Numeric,2);
Round
-------
0.25
(1 row)

Note: After the type conversion, you can retain the fractional part.

--3 can also be converted by the cast function
postgres=# Select Round (CAST (1 as numeric)/cast (4 as numeric), 2);
Round
-------
0.25
(1 row)

--4 about the use of the cast function
postgres=# SELECT substr (CAST (1234 as text), 3,1);
Substr
--------
3
(1 row)

Postgres Type Conversion Cast