Rapid postgresql learning, part 4

Rapid POSTGRESQL learning, PART-5BY: ALI MASUDIANPOUR [email protected]

RAPID POSTGRESQL LEARNING. 1

mailto:[email protected]

Transactions◦ Transactions are a group of SQL commands

◦ These commands will be group together as an operation

◦ Transactions are supposed to be ACID, but what does that mean?◦ ACID: Atomicity, Consistency, Isolation, Durability

◦ ATOMICITY

◦ All or nothing

◦ All of the operations must be succeed or all fails. In other word if one command fails other will fail too

◦ CONSYSTENCY

◦ Means that any transaction should take the system from one consistency o another

◦ In other words, only valid changes to the data will take a place

◦ ISOLATION

◦ Any pear of transactions should not be effecting the same row at once

◦ DURABILITY

◦ Once the transaction is committed, its result will not be lost forever


Transactions◦ Working with transactions (KEYWORDS)

◦ To begin transaction:

◦ BEGIN

◦ To end transaction

◦ COMMIT

◦ To cancel transaction

◦ ROLLBACK

◦ Example◦ BEGIN;

SELECT * FROM [table name]COMMIT;

◦ Control Transactions◦ It is possible to control the commit in transactions using SAVEPOINT


Save points◦ Save points allow us to commit part of transaction and discard other parts

◦ How to use SAVE POINT:◦ BEGIN

UPDATE x SET y=20 WHERE 1SAVEPOINT [save point name]UPDATE z SET a=14 WHERE 1SOLLBACK TO SAVEPOINT [save point name]COMMIT;

◦ Everything before save point will be committed and everything after save point will be discarded

◦ Destroy SAVE POINT◦ To destroy a save point we use RELEASE

◦ RELEASE SAVEPOINT [save point name]

◦ After deletion of save point if we try to ROLLBACK TO SAVEPOINT [save point name] it will show an error!


DEADLOCKS◦ A deadlock happens when two or more transactions hold locks at other transactions at once

◦ As we saw before, same operations on same rows in transaction can not be happen

◦ If we do, it will be wait until first transaction done.

◦ DEADLOCK◦ For instance: if we start a transaction one[1] and after that start the transaction two[2] and in transaction two[2] we write a

command that will be wait for transaction one[1] to be done and after that we do the same in transaction one[1] deadlock will be happen.

◦ At this moment we have to ROLLBACK

◦ If we try to COMMIT, it will automatically ROLLBACK


System Columns◦ Columns that are added to the table automatically called System Columns

◦ List of System Columns◦ XMIN

◦ Transaction id of the inserting transaction for this row version. It also can be update

◦ ROW VERSION

◦ Is an individual state of a row. Every time we update the row, new row version will be generated

◦ XMAX

◦ Transaction id of deletion row

◦ CTID

◦ Physical location of the row version in the table

◦ OIDS

◦ Table object id

◦ If we want to use OIDS, we should indicate in on the table creation time

◦ CREATE TABLE … WITH OIDS;

◦ Examples:◦ SELECT oid, tableoid, xmax, xmin FROM [table name]


Alternation in tables and columns◦ Change data type of column

◦ ALTER [table name] ALTER COLUMN [column name] TYPE [new type]

◦ Change default value of column◦ ALTER TABLE [table name] ALTER COLUMN [column name] SET DEFAULT [value];

◦ Unset default value◦ ALTER TABLE [table name] ALTER COLUMN [column name] SET DEFAULT NULL

◦ ALTER TABLE [table name] ALTER COLUMN [column name] DROP DEFAULT

◦ Add Column◦ ALTER TABLE [table name] ADD COLUMN [column name] [column type]

◦ ALTER TABLE [table name] ADD COLUMN [column name] [column type] NOT NULL DEFAULT [value]

◦ Remove Column◦ ALTER TABLE [table name] DROP COLUMN [column name]

◦ Every data and constraints will be deleted

◦ If it has a reference column, we must use CASCADE to remove


Alternation in tables and columns◦ Add Constraint

◦ CHECK

◦ ALTER TABLE [table name] ADD CONSTRAINT [constraint name] CHECK([condition])

◦ UNIQUE

◦ ALTER TABLE [table name] ADD CONSTRAINT [constraint name] UNIQUE ([column name])

◦ FOREIGN KEY

◦ ALTER TABLE [table name] ADD FOREIGN KEY [foreign key name] REFERENCES [reference table name]([reference table column name])

◦ NOT NULL

◦ ALTER TABLE [table name] ALTER COLUMN [column name] SET NOT NULL

◦ All of the values must satisfy constraints to be done◦ For instance we have a column that holds null value, now if we set null constraint it will generate an error, because it has a null

value.


Alternation in tables and columns◦ Remove Constraint

◦ ALTER TABLE [table name] DROP CONSTRAINT [constraint name]

◦ If it uses a reference we should use CASCADE

◦ Remove Not Null Constraint◦ ALTER TABLE [table name] ALTER COLUMN [column name] DROP NOT NULL

◦ Rename Column name◦ ALTER TABLE [table name] RENAME COLUMN [column name] TO [new column name]

◦ Rename Table name◦ ALTER TABLE [table name] RENAME TO [new table name]


Logical Operators◦ 3 types of Logical operators

◦ AND

◦ Will be true if both left and right operands are true

◦ OR

◦ Will be true if one of the operands is true, otherwise it will be false

◦ NOT

◦ Will be false if the operand is true and will be true if the operand is false

◦ AND / OR has 2 right and left operand

◦ NOT has one operand

◦ Examples:◦ SELECT * FROM tableTest WHERE x>12 AND y<10

◦ SELECT * FROM tableTest WHERE x>12 OR y<10

◦ SELECT * FROM tableTest WHERE NOT x>12


Comparison Operands◦ They are

◦ <

◦ <=

◦ >

◦ >=

◦ =

◦ !

◦ Examples ◦ SELECT * FROM testable WHERE column1!=3600

◦ SELECT * FROM testable WHERE column1=3600

◦ SELECT * FROM testable WHERE column1>=3600

◦ SELECT * FROM testable WHERE column1<=3600

◦ SELECT * FROM testable WHERE column1>3600

◦ SELECT * FROM testable WHERE column1<3600


Between◦ Between

◦ To run a condition between a range

◦ Example:

◦ SELECT * FROM employee WHERE salary BETWEEN 2000 AND 9000

◦ The less value should be take place in left side of AND operator

◦ SYMETRIC BETWEEN◦ In this case there would be no force to left operand be greater than right operand

◦ Example

◦ SELECT * FROM employee WHERE salary BETWEEN SYMETRIC 9000 AND 2000

◦ NOT BETWEEN◦ SELECT * FROM employee WHERE salary NOT BETWEEN 5000 AND 6000


IS NULL/ IS NOT NULL◦ SELECT * FROM employee WHERE salary IS NULL

◦ SELECT * FROM employee WHERE salary IS NOT NULL

◦ SELECT * FROM employee WHERE (salary>3000) IS TRUE

◦ SELECT * FROM employee WHERE (salary>3000) IS NOT TRUE

◦ SELECT * FROM employee WHERE (salary>3000) IS FALSE

◦ SELECT * FROM employee WHERE (salary>3000) IS NOT FALSE

◦ SELECT * FROM employee WHERE (salary>3000) IS UNKNOWN

◦ SELECT * FROM employee WHERE (salary>3000) IS NOT UNKNOWN


Mathematical Operators◦ Addition

◦ SELECT 7+3

◦ Subtraction◦ SELECT 7-3

◦ Multiplication◦ SELECT 7*3

◦ Division◦ SELECT 7/3

◦ Modulo◦ SELECT 7%3

◦ Exponentiation◦ SELECT 7^3

◦ Square Root◦ SELECT |/4

◦ Cube root◦ SELECT ||/8

◦ Factorial◦ SELECT 7! AD ‘Factorial’


Mathematical Functions◦ Natural Logarithm

◦ SELECT ln(4)

◦ Base 10 logarithm◦ SELECT log(8)

◦ PI Constant◦ SELECT pi() AS ‘PI’

◦ Power◦ SELECT power(2,3)

◦ Round◦ SELECT round(2.888888)

◦ Truncate◦ SELECT TRUNC(2.567,2) // truncate to 2 decimal points. Result : 2.56

◦ SELECT TRUNC(2.567) // result: 2


Mathematical Functions◦ Floor

◦ Largest integer not greater than entered value

◦ SELECT FLOOR(4.5)

◦ Result: 4

◦ CEIL◦ Smallest integer not less that entered value

◦ SELECT CEIL(4.5)

◦ Result: 5

◦ Absolute value◦ SELECT abs(-4.88)

◦ Division◦ SELECT DIV(4,7)

◦ Modulo◦ SELECT MOD(4,5)

◦ Square root◦ SELECT SQRT(25)

◦ Cube Root◦ SELECT CBRT(45)


END OF PART 4End of Part 4◦ In part 5 we will discuss about:

◦ STRING FUNCTIONS AND OPERATIONS

◦ DATE AND TIME

◦ SEQUENCES

◦ CONDITIONAL EXPRESSIONS

◦ SCHEMA and PRIVILEGES

◦ INDEXES


Rapid postgresql learning, part 4

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Transcript of Rapid postgresql learning, part 4