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Some Basic sql(oracle) queries for beginners
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SQL(Oracle) QueriesDDL (Data definition language)
TABLE
Create table CREATE TABLE <table_name> (< column_name1> <datatype> [<constraint>], < column_name2> <datatype> [<constraint>],…);
Show tables list Select * from TAB;Describe table(table structure) DESCRIBE <table_name>;Delete/Drop table DROP TABLE <table_name>;Rename table RENAME <old_table_name>TO
<new_table_name>;
COLUMN
CONSTRAINTS
Constraints
Add constraint Drop constraint
Not null ALTER TABLE <table name>MODIFY <column_name>CONSTRAINT <constraint_name>NOT NULL;;
ALTER TABLE <table name> MODIFY <column_name> NULL;
Unique ALTER TABLE <table name>ADD CONSTRAINT <constraint_name>UNIQUE (<column_name>);
ALTER TABLE <table name>DROP CONSTRAINT <constraint_name>;
Check ALTER TABLE <table name>ADD CONSTRAINT <constraint_name>CHECK (<column_name><condition>);
ALTER TABLE <table name>DROP CONSTRAINT <constraint_name>;
Primary key
ALTER TABLE <table name>ADD CONSTRAINT
ALTER TABLE <table name>
Add a column ALTER TABLE <table name>ADD <new_column_name> <datatype> [<constraint>];
Rename a column ALTER TABLE <table name>RENAME COLUMN <old_column_name> TO <new_column_name>;
Delete a column ALTER TABLE <table name>DROP <column_name>;
Modify datatype or size
ALTER TABLE <table name>MODIFY <column_name> <datatype> [<constraint>];
<constraint_name>PRIMARY KEY (<column_name>);
DROP CONSTRAINT <constraint_name>;
Default ALTER TABLE <table name>MODIFY <column_name> DEFAULT <value>;
ALTER TABLE <table name>MODIFY <column_name> DEFAULT NULL;
Foreign key
ALTER TABLE <table name>ADD CONSTRAINT <constraint_name>FOREIGN KEY (<column_name> )REFERENCES <table name1> (<column_name> );
ALTER TABLE <table name>DROP CONSTRAINT <constraint_name>;
DML (Data Manipulation language)
INSERT
Insert into all columns INSERT INTO <table_name>VALUES (<column1_value>,< column2_value>,……);
Insert into specific columns
INSERT INTO <table_name> (<column1>, <column2>,…)VALUES (<column1_value>, <column2_value>,……);
SELECT
Select all data (all rows all columns – full table)
SELECT * FROM <table_name>;
Select specific columns SELECT <column1, column2,….>FROM <table_name>;
Select all data based on condition
SELECT *FROM <table_name> WHERE <condition>;
Select data in ascending/descending order
SELECT *FROM <table_name>ORDER BY <column1><ascending/descending>;
UPDATE
Update values which satisfy condition
UPDATE <table_name> SET <column_name>=<new_value>;
Update all values of a specific column(same values for a particular column)
UPDATE <table_name>SET <column_name>=<new_value>WHERE <condition>;
DELETE
Delete specific rows based on condition
DELETEFROM <table_name>WHERE <condition>;
Clear all data of a table(delete all rows)
DELETEFROM <table_name>;
Identifiers-An Identifier is essentially a name of a database_name, table_name, column_name or constraint_name.
Rules-1. First letter must be alphabet (a-z, A-Z).2. Second and other letters can be numbers (0-9), alphabet (a-z, A-Z) and _
(underscore).3. Must not be a keyword.