Some Basic sql(oracle) queries for beginners

1. SQL(Oracle) Queries
DDL (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>;
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>];
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 <constraint_name>
PRIMARY KEY (<column_name>);
ALTER TABLE <table 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>;

2. 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 DELETE
FROM <table_name>
WHERE<condition>;
Clear all data of a table(delete all rows) DELETE
FROM <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.