Oracle (CAST, TO_CHAR, to_date) usage

Cast:

Cast (the value to be converted as the type of the conversion)

from to Number

	to Binary_float, binary_double	to CHAR, VARCHAR2		to DATETIME, INTERVAL	to NCHAR, NVARCHAR2
Binary_float, binary_double	Yes	Yes	Yes	No	Yes
CHAR, VARCHAR2	Yes	Yes	Yes	Yes	No
Number	Yes	Yes	Yes	No	Yes
DATETIME, INTERVAL	No	Yes	No	Yes	Yes
NCHAR, NVARCHAR2	Yes	No	Yes	No	Yes

Example

CAST(‘123.4567‘ AS NUMBER(10,2))Returns the value 123.46 .

From the above description, we can know that cast can convert one type to another.

For example, converting a string type to a number (10,2) type, and not just to using To_number, To_char (), and to_date () types, table 3-1 above represents whether cast can be used for this type of mutual conversions.

Example calls:

Chenzw> SELECT CAST (' 123.4567 ' as Number (10,2)) as NUM from DUAL; Output 123.46

To_char:

Convert to String type
SELECT to_char (sysdate, ' Yyyy/mm/dd HH24:mi:ss ') from DUAL

Sysdate: The value to be converted, followed by the type of the spin (string type)

function	return	Description	Example
To_char (timestamp, text)	Text	Convert Timestamp to String	To_char (timestamp ' Now ', ' HH12:MI:SS ')
To_char (int, text)	Text	Convert Int4/int8 to String	To_char (125, ' 999 ')
To_char (Float, text)	Text	Convert Float4/float8 to String	To_char (125.8, ' 999d9 ')
To_char (Numeric, text)	Text	Convert numeric to String	To_char (Numeric ' -125.8 ', ' 999d99s ')
To_date (text, text)	Date	Convert String to date	To_date (' Dec ', ' DD Mon YYYY ')
To_timestamp (text, text)	Date	Convert String to Timestamp	To_timestamp (' Dec ', ' DD Mon YYYY ')
To_number (text, text)	Numeric	Convert string to Numeric	To_number (' 12,454.8-', ' 99g999d9s ')

To_date: Converts a value to a date type.

SELECT to_date (' 2007-06-12 10:00:00 ', ' yyyy/mm/dd HH24:mi:ss ') from DUAL to output 2007/6/12 Tuesday 10:00:00

Oracle (CAST, TO_CHAR, to_date) usage