DATABASE SYSTEM SQL

CREATE

Creates the main components of a database, such as databases and tables.

DROP

Deletes tables or databases permanently.

ALTER

Modifies existing structures, like adding, deleting, or changing columns.

INSERT

Loads or adds new data into the database.

UPDATE

Modifies the values of specified fields and records.

DELETE

Deletes specific records from a database table.

GRANT

Gives permissions to users.

REVOKE

Removes permissions from users.

COMMIT

Confirms an operation or transaction.

ROLLBACK

Rewinds or undoes an operation.

SELECT

Used to query database records that satisfy a given criterion and specify the columns to be included in the results.

FROM

Specifies the relationships or tables to be used as the source for the query.

WHERE

Specifies filter conditions that the rows must meet to be selected.

ORDER BY

Sorts the selected data results, typically in ascending (ASC) or descending (DESC) order.

GROUP BY

Groups rows with identical values in specified columns into summary rows.

HAVING

Filters results after they have been grouped.

LIMIT

Restricts the number of rows or items returned by the query.

=, <>, !=, >, >=,

Standard comparison operators to check if values are equal, different, larger, or smaller.

Safely compares equality, even handling NULL values.

AND / OR

Logical operators used to combine multiple filtering conditions.

IN ( )

Checks if a value matches any value within a specified list.

NOT

Denies or reverses a condition.

BETWEEN

Checks if values fall within a specific range, including the extremes.

IS NULL / IS NOT NULL

Checks if a value is empty (NULL) or has data.

LIKE

Defines a search pattern. Uses % to represent zero, one, or multiple characters, and _ to represent one specific character.

EXISTS

A condition that is met if a subquery returns at least one row.

DISTINCT

Filters the data to select and return only unique (non-repeated) values.

INNER JOIN

Finds matches between two tables, returning only records that have identical values in the linked fields.

LEFT (OUTER) JOIN

Returns all rows from the left table, even if there is no matching row in the right table (putting NULL in the unmatched right columns).

RIGHT (OUTER) JOIN

Returns all rows from the right table, even if there is no matching row in the left table.

FULL (OUTER) JOIN

Returns all rows from both tables, even if they have no correspondence in the other table.

CROSS JOIN

Generates all combinations of records (Cartesian Product) between two tables.

UNION

Merges two tables together without showing duplicate records (requires matching columns and data types).

UNION ALL

Merges two tables and shows everything, including duplicates.

INTERSECT

Keeps only the rows that are common to both queries.

EXCEPT

Generates only the records that are unique to the first table.

COUNT

Returns the total number of rows selected by the query.

MIN

Returns the minimum value of a specified field.

MAX

Returns the maximum value of a specified field.

SUM

Adds the values of a specified field.

AVG

Returns the average value of a specified field.

LOWER / LCASE

Converts a string to lower case.

UPPER / UCASE

Converts a string to upper case.

TRIM, RTRIM, LTRIM

Removes spaces from a string.

LEFT / RIGHT

Extracts a specific number of characters from the left (beginning) or right (end) of a string.

CONCAT

Joins multiple strings together to form a new string.

REPLACE

Swaps specified sequences of characters with a new string.

SUBSTRING

Extracts a portion of a string.

LENGTH

Returns the total number of characters in a string.

NOW()

Returns the constant date and time at the exact moment the statement starts executing.

SYSDATE()

Returns the date and time of the server dynamically each time the function is evaluated.

CURRENT_DATE()

Returns the current date of the client.

DATE_ADD() / DATE_SUB()

Adds or subtracts a specified interval (minutes, hours, days) from a date value.