Table Of Contents :
What is SQL ?
SQL (pronounced "ess-que-el") stands for Structured Query Language. SQL is used to communicate with a database. According to ANSI (American National Standards Institute), it is the standard language for relational database management systems. In this blog we will learn about MANAGING TRIGGERS, MANAGING INDEXES, MANAGING VIEWS, MODIFYING DATA, USING SQL CONSTRAINTS, MANAGING TABLES, USING SQL OPERATORS, QUERYING FROM MULTIPLE TABLES, QUERYING DATA FROM A TABLE and etc. ou will also learn about SQL, SQL server and etc.
QUERYING DATA FROM A TABLE
SELECT c1, c2 FROM t;
Query data in columns c1, c2 from a table
SELECT * FROM t;
Query all rows and columns from a table
SELECT c1, c2 FROM t
WHERE condition;
Query data and filter rows with a condition
SELECT DISTINCT c1 FROM t
WHERE condition;
Query distinct rows from a table
SELECT c1, c2 FROM t
ORDER BY c1 ASC [DESC];
Sort the result set in ascending or descending order
SELECT c1, c2 FROM t
ORDER BY c1
LIMIT n OFFSET offset
Skip offset of rows and return the next n rows
SELECT c1, aggregate(c2)
FROM t
GROUP BY c1;
Group rows using an aggregate function
SELECT c1, aggregate(c2)
FROM t
GROUP BY c1
HAVING condition;
Filter groups using HAVING clause
QUERYING FROM MULTIPLE TABLES
SELECT c1, c2
FROM t1
INNER JOIN t2 ON condition;
Inner join t1 and t2
SELECT c1, c2
FROM t1
LEFT JOIN t2 ON condition;
Left join t1 and t1
SELECT c1, c2
FROM t1
FULL OUTER JOIN t2 ON condition;
Perform full outer join
SELECT c1, c2
FROM t1
CROSS JOIN t2;
Produce a Cartesian product of rows in tables
SELECT c1, c2
FROM t1 A
INNER JOIN t2 B ON condition;
Join t1 to itself using INNER JOIN clause
USING SQL OPERATORS
SELECT c1, c2 FROM t1
UNION [ALL]
SELECT c1, c2 FROM t2;
Combine rows from two queries
SELECT c1, c2 FROM t1
INTERSECT
SELECT c1, c2 FROM t2;
Return the intersection of two queries
SELECT c1, c2 FROM t1
MINUS
SELECT c1, c2 FROM t2;
Subtract a result set from another result set
SELECT c1, c2 FROM t1
WHERE c1 [NOT] LIKE pattern;
Query rows using pattern matching %, _
SELECT c1, c2 FROM t
WHERE c1 [NOT] IN value_list;
Query rows in a list
SELECT c1, c2 FROM t
WHERE c1 BETWEEN low AND high;
Query rows between two values
SELECT c1, c2 FROM t
WHERE c1 IS [NOT] NULL;
Check if values in a table is NULL or not
MANAGING TABLES
CREATE TABLE t (
 id INT PRIMARY KEY,
 name VARCHAR NOT NULL,
 price INT DEFAULT 0
);
Create a new table with three columns
DROP TABLE t ;
Delete the table from the database
ALTER TABLE t ADD column;
Add a new column to the table
ALTER TABLE t DROP COLUMN c ;
Drop column c from the table
ALTER TABLE t ADD constraint;
Add a constraint
ALTER TABLE t DROP constraint;
Drop a constraint
Alter TABLE t1 RENAME TO t2;
Rename a table from t1 to t2
ALTER TABLE t1 RENAME c1 TO c2 ;
Rename column c1 to c2
TRUNCATE TABLE t;
Remove all data in a table
USING SQL CONSTRAINTS
CREATE TABLE t(
 c1 INT, c2 INT, c3 VARCHAR,
 PRIMARY KEY (c1,c2)
);
Set c1 and c2 as a primary key
CREATE TABLE t1(
 c1 INT PRIMARY KEY,
 c2 INT,
FOREIGN KEY (c2) REFERENCES t2(c2)
);
Set c2 column as a foreign key
CREATE TABLE t(
 c1 INT, c1 INT,
 UNIQUE(c2,c3)
);
Make the values in c1 and c2 unique
CREATE TABLE t(
 c1 INT, c2 INT,
CHECK(c1> 0 AND c1 >= c2)
);
Ensure c1 > 0 and values in c1 >= c2
CREATE TABLE t(
 c1 INT PRIMARY KEY,
 c2 VARCHAR NOT NULL
);
Set values in c2 column not NULL
MODIFYING DATA
INSERT INTO t(column_list)
VALUES(value_list);
Insert one row into a table
INSERT INTO t(column_list)
VALUES (value_list),
(value_list), ....;
Insert multiple rows into a table
INSERT INTO t1(column_list)
SELECT column_list
FROM t2;
Insert rows from t2 into t1
UPDATE t
SET c1 = new_value;
Update new value in the column c1 for all rows
UPDATE t
SET c1 = new_value,
c2 = new_value
WHERE condition;
Update values in the column c1, c2 that match
the condition
DELETE FROM t;
Delete all data in a table
DELETE FROM t
WHERE condition;
Delete subset of rows in a table
MANAGING VIEWS
CREATE VIEW v(c1,c2)
AS
SELECT c1, c2
FROM t;
Create a new view that consists of c1 and c2
CREATE VIEW v(c1,c2)
AS
SELECT c1, c2
FROM t;
WITH [CASCADED | LOCAL] CHECK OPTION;
Create a new view with check option
CREATE RECURSIVE VIEW v
AS
select-statement -- anchor part
UNION [ALL]
select-statement; -- recursive part
Create a recursive view
CREATE TEMPORARY VIEW v
AS
SELECT c1, c2
FROM t;
Create a temporary view
DROP VIEW view_name
Delete a view
MANAGING INDEXES
CREATE INDEX idx_name
ON t(c1,c2);
Create an index on c1 and c2 of the table t
CREATE UNIQUE INDEX idx_name
ON t(c3,c4);
Create a unique index on c3, c4 of the table t
DROP INDEX idx_name;
Drop an index
SQL AGGREGATE FUNCTIONS
AVG returns the average of a list
COUNT returns the number of elements of a list
SUM returns the total of a list
MAX returns the maximum value in a list
MIN returns the minimum value in a list
MANAGING TRIGGERS
CREATE OR MODIFY TRIGGER trigger_name
WHEN EVENT
ON table_name TRIGGER_TYPE
EXECUTE stored_procedure;
Create or modify a trigger
WHEN
• BEFORE – invoke before the event occurs
• AFTER – invoke after the event occurs
EVENT
• INSERT – invoke for INSERT
• UPDATE – invoke for UPDATE
• DELETE – invoke for DELETE
TRIGGER_TYPE
• FOR EACH ROW
• FOR EACH STATEMENT
CREATE TRIGGER before_insert_person
BEFORE INSERT
ON person FOR EACH ROW
EXECUTE stored_procedure;
Create a trigger invoked before a new row is
inserted into the person table
DROP TRIGGER trigger_name
Delete a specific trigger
