#Pl-Sql

To find the constraints in a table

ALL_CONSTRAINTS: Provides information about all constraints accessible to the user, across all tables in the database. It includes constraint types, status, and more, but doesn’t show column-specific details.

SELECT * FROM ALL_CONSTRAINTS 
WHERE TABLE_NAME='YOUR_TABLE_NAME' 
AND OWNER = 'OWNER_NAME';

To find the constarints referring to a table.

SELECT * FROM ALL_CONSTRAINTS 
WHERE R_CONSTRAINT_NAME IN ( 
    SELECT CONSTRAINT_NAME FROM ALL_CONSTRAINTS 
    WHERE TABLE_NAME='YOUR_TABLE_NAME' 
    )
AND OWNER = 'OWNER_NAME';

USER_CONS_COLUMNS: Shows details about columns associated with constraints for tables owned by the current user. It’s useful for checking specific columns involved in constraints like primary keys, foreign keys, or unique constraints.

SELECT CONSTRAINT_NAME, TABLE_NAME, COLUMN_NAME, POSITION
FROM USER_CONS_COLUMNS
WHERE TABLE_NAME = 'YOUR_TABLE_NAME';

The RETURNING INTO clause allows us to return column values for rows affected by DML statements. The returned data could be a single column, multiple columns or expressions.

INSERT INTO t1 VALUES (t1_seq.nextval, 'FOUR')
RETURNING id INTO l_id;

References

Oracle, dba-oracle, oracle base

This view describes all directories accessible to the user.

SELECT * FROM ALL_DIRECTORIES;

This view describes all directories specified for the entire database.

SELECT * FROM DBA_DIRECTORIES;

To view all the tables details, look here.

References

Oracle Doc

The TIMESTAMP datatype is an extension on the DATE datatype. In addition to the datetime elements of the DATE datatype, the TIMESTAMP datatype holds fractions of a second to a precision between zero and nine decimal places, the default being six. There are also two variants called TIMESTAMP WITH TIME ZONE and TIMESTAMP WITH LOCAL TIME ZONE. As their names imply, these timestamps also store time zone offset information.

create table table_name (
    column_name number,
    column_name2 timestamp default systimestamp);

References

dba-oracle
dba-oracle 2

To move a table to the recycle bin or remove it entirely from the database, you use the DROP TABLE statement:

DROP TABLE schema_name.table_name
[CASCADE CONSTRAINTS | PURGE];

• First, indicate the table and its schema that you want to drop after the DROP TABLE clause. If you don’t specify the schema name explicitly, the statement assumes that you are removing the table from your own schema.

• Second, specify CASCADE CONSTRAINTS clause to remove all referential integrity constraints which refer to primary and unique keys in the table. In case such referential integrity constraints exist and you don’t use this clause, Oracle returns an error and stops removing the table.

• Third, specify PURGE clause if you want to drop the table and release the space associated with it at once. By using the PURGE clause, Oracle will not place the table and its dependent objects into the recycle bin.

Refernces

oracle tutorial

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.

When using binary collations there are three suffixes that alter the behavior 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.

// Syntax
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;

References

Oracle Base, Oracle Doc

The NLS_DATABASE_PARAMETERS shows the values of the NLS parameters for the database. Oracle notes these differences between the parameters.

• NLS_SESSION_PARAMETERS shows the NLS parameters and their values for the session that is querying the view. It does not show information about the character set.
• NLS_INSTANCE_PARAMETERS shows the current NLS instance parameters that have been explicitly set and the values of the NLS instance parameters.
• NLS_DATABASE_PARAMETERS shows the values of the NLS parameters for the database. The values are stored in the database.

SELECT * FROM NLS_SESSION_PARAMETERS ORDER BY 1;   
SELECT * FROM NLS_INSTANCE_PARAMETERS ORDER BY 1;  
SELECT * FROM NLS_DATABASE_PARAMETERS ORDER BY 1; 

The NLS_LANGUAGE and NLS_TERRITORY values in NLS_DATABASE_PARAMETERS cannot be changed once the database has been created

References

dba-oracle
Oracle Blog