Collation determines how strings are compared, which has a direct impact on ordering (sorting) and equality tests between strings.
There are two basic types of collation.
- Binary : Ordering and comparisons of string data are based on the numeric value of the characters in the strings.
- Linguistic : Ordering and comparisons of string data are based on the alphabetic sequence of the characters, regardless of their numeric values. The list of linguistic collations is available here.
When using collations there are three suffixes that alter the behaviour of sorts and comparisons.
- “_CI” : Case insensitive, but accent sensitive.
- “_AI” : Both case and accent insensitive.
- “_CS” : Both case and accent sensitive. This is default if no extension is used.
If no collation is specified, directly or via a default setting, the default USING_NLS_COMP pseudo-collation is used, which means the NLS_SORT and NLS_COMP parameters are used to determine the actual collation used.
COLLATE BINARY_CS / BINARY_CI / BINARY_AI
column_name VARCHAR2(15 CHAR) COLLATE BINARY_CI
create table (...) DEFAULT COLLATION BINARY_CI;
ALTER TABLE t1 DEFAULT COLLATION BINARY_AI;