7.1 KiB
❄ PostgreSQL CHEAT SHEET
🧐 What is PostgreSQL?
PostgreSQL/Postgres is a free open-source relational database management system(RDBMS) emphasizing extensibility and SQL compliance. It was originally named POSTGRES, referring to it's origins as a successor to the Ingres database developed at the University of California, Berkeley.
🤔 What is the use of PostgreSQL?
It is a highly stable database management system, backend by more than 20 years of community development which has contributed to it's high levels of resilience, integrity, and correctness. PostgreSQL is used as the primary data store or data warehouse for many web, mobile, geospatial, and analytics applications.
📚 PostgreSQL Table of Contents
1️⃣ QUERYING DATA FROM A TABLE
View Queries
SELECT c1, c2 FROM t;
Query data in columns c1, c2 form 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 in aggregate function
SELECT c1, aggregate(c2)
FROM t
GROUP BY c1
HAVING condition;
Filter groups using HAVING clause
2️⃣ QUERYING FROM MULTIPLE TABLES
View Queries
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
RIGHT JOIN t2 ON condition;
Right join t1 and t2
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, t2;
Another way to perform cross join
SELECT c1, c2
FROM t1 A
INNER JOIN t2 B ON condition;
Join t1 to itself using INNER JOIN clause
3️⃣ USING SQL OPERATORS
View Queries
SELECT c1, c2
FROM t1
UNION [ALL]
SELECT c1, c2 FROM t2;
Combine rows from tow queries
SELECT c1, c2 FROM t1
INTERSECT
SELECT c1, c2 FROM t2;
Return the intersection of two queries
SELECT c1, c2 FROM t1
EXCEPT
SELECT c1,c2 FROM t2;
Subtract a result set from another result set
SELECT c1, c2 FROM t
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_value AND high_value;
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
4️⃣ MANAGING TABLES
View Queries
CREATE TABLE(
id SERIAL PRIMARY KEY,
name VARCHAR NOT NULL,
price NUMERIC(10,2) DEFAULT 0
);
Create a new table with three columns
DROP TABLE t CASCADE;
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 contraint;
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 CASCADE;
Remove all data in a table
5️⃣ USING SQL CONSTRAINTS
View Queries
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 SERIAL PRIMARY KEY,
c2 INT,
FOREIGN KEY (c2) REFERENCES ts(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, c INT,
CHECK(c1 > 0 AND c1 >= c2)
);
Ensure c1 > 0 and values in c1 >= c2
CREATE TABLE t(
c1 SERIAL PRIMARY KEY,
c2 VARCHAR NOT NULL
);
Set values in c2 column not null
6️⃣ MODIFIYING DATA
View Queries
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
7️⃣ MANAGING VIEWS
View Queries
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
8️⃣ MANAGING INDEXES
View Queries
CREATE INDEX inx_name
ON t(c1, c2);
Create an index on c1 and c2 of the table t
CREATE UNIQUE INDEX inx_name
ON t(c3, c4);
Create unique index on c3, c4 of the table t
DROP INDEX idx_name;
Drop an index
9️⃣ MANAGING TRIGGERS
View Queries
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
🔟 SQL AGGREGATE FUNCTIONS
View Queries
- 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