SQL in Brief

SQL 
It eases the burden of programmer and other user’s as they need to know how or where data is stored..They just have to specify what is required and how the specific data set to be presented. It is just like querying in simple English which allow the user to specify how the human conceptualizes the query in the mind.

SQL Syntax Introduction


2. CREATE TABLE syntax
CREATE TABLE [ IF NOT EXISTS ] table_name
( column_declare1, column_declare2, constraint_declare1, … )
column_declare ::= column_name type [ DEFAULT expression ]
[ NULL | NOT NULL ] [ INDEX_BLIST | INDEX_NONE ]
type ::= BIT | REAL | CHAR | TEXT | DATE | TIME |
FLOAT | BIGINT | DOUBLE | STRING | BINARY | NUMERIC |
DECIMAL | BOOLEAN | TINYINT | INTEGER | VARCHAR |
SMALLINT | VARBINARY | TIMESTAMP | LONGVARCHAR |
JAVA_OBJECT | LONGVARBINARY
constraint_declare :: = [ CONSTRAINT constraint_name ]
PRIMARY KEY ( col1, col2, … ) |
FOREIGN KEY ( col1, col2, … ) REFERENCES f_table [ ( col1, col2, … ) ]
[ ON UPDATE triggered_action ] [ ON DELETE triggered_action ] |
UNIQUE ( col1, col2, … ) |
CHECK ( expression )
[ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
[ NOT DEFERRABLE | DEFERRABLE ]
triggered_action :: =
NO ACTION | SET NULL | SET DEFAULT | CASCADE
When declaring string or binary column types the maximum size must be specified. The following example declares a string column that can grow to a maximum of 100 characters,
CREATE TABLE Table ( str_col VARCHAR(100) )
When handling strings the database will only allocate as much storage space as the string uses up. If a 10 character string is stored in str_col then only space for 10 characters will be allocated in the database. So if you need a column that can store a string of any size, use an arbitrarily large number when declaring the column. Mckoi SQL Database does not use a fixed size storage mechanism when storing variable length column data.
JAVA_OBJECT is a column type that can contain serializable Java objects. TheJAVA_OBJECT type has an optional Java class definition that is used for runtime class constraint checking. The following example demonstrates creating aJAVA_OBJECT column.
CREATE TABLE ObjectTable (
obj_id NUMERIC, obj JAVA_OBJECT(java.awt.Point))
If the Java class is not specified the column defaults to java.lang.Object which effectively means any type of serializable Java object can be kept in the column.
String types may have a COLLATE clause that changes the collation ordering of the string based on a language. For example, the folling statement creates a string that can store and order Japanese text;
CREATE TABLE InternationalTable (
japanese_text VARCHAR(4000) COLLATE ‘jaJP’)
The ‘jaJP’ is an ISO localization code for the Japanese language in Japan. Other locale codes can be found in the documentation to java.text.Collate.
Unique, primary/foreign key and check integrity constraints can be defined in theCREATE TABLE statement. The following is an example of defining a table with integrity constraints.
CREATE TABLE Customer (
number VARCHAR(40)  NOT NULL,
name   VARCHAR(100) NOT NULL,
ssn    VARCHAR(50)  NOT NULL,
age    INTEGER      NOT NULL,
CONSTRAINT cust_pk PRIMARY KEY (number),
UNIQUE ( ssn ),              // (An anonymous constraint)
CONSTRAINT age_check CHECK (age >= 0 AND age < 200)
)


3. ALTER TABLE syntax
ALTER TABLE table_name ADD [COLUMN] column_declare
ALTER TABLE table_name ADD constraint_declare
ALTER TABLE table_name DROP [COLUMN] column_name
ALTER TABLE table_name DROP CONSTRAINT constraint_name
ALTER TABLE table_name DROP PRIMARY KEY
ALTER TABLE table_name ALTER [COLUMN] column_name SET default_expr
ALTER TABLE table_name ALTER [COLUMN] column_name DROP DEFAULT
ALTER CREATE TABLE ….
ALTER is used to add / remove / modify the columns and integrity constraints of a table. The ADD [COLUMN] form adds a new column definition to the table (using the same column declaration syntax in the CREATE command). The DROP [COLUMN]form drops the column with the name from the table. ALTER [COLUMN] column_name SET default_expr alters the default value for the column. ALTER [COLUMN] column_name DROP DEFAULT removes the default value set for the column.
The following example adds a new column to a table;
ALTER TABLE Order ADD notes VARCHAR(60000) DEFAULT ‘n/a’
ADD constraint_declare is used to define a new integrity constraint on a table (using the same constraint declaration syntax in the CREATE command). DROP CONSTRAINT is used to drop a named constraint from a table.
The other form of this statement is ALTER CREATE TABLE …. This alters the table to the specification of the given CREATE statement. Any columns that are in the original table are not lost provided the column name is in the new table specification. Any columns that were not in the original table are set to the default value.
The following example demonstrates this form of ALTER statement;
ALTER CREATE TABLE table
( col1 INTEGER NOT NULL UNIQUE,
col2 NUMERIC,
col3 VARCHAR(90000) )
The ALTER CREATE TABLE … syntax is an extension to the SQL-92 standard.

4. DROP TABLE syntax

DROP TABLE [ IF EXISTS ] table_name1, table_name2, ….
Removes the table(s) from the database. The IF EXISTS clause will drop the table only if it exists. If this clause is not present an error is generated if the table does not exist. Any data that was in a dropped table is lost so use with care.

5. CREATE VIEW syntax

CREATE VIEW table_name [ ( column_name1, column_name2, … ) ]
AS SELECT …
Creates a new view. A view is a virtual table based on the result of a SELECTquery. The content of a view may reference any number of other tables and views.
A simple example of a view follows;
CREATE VIEW ViewOfTableA AS SELECT col1 FROM TableA
A view acts like a regular table and can be queried as you would a table made with the CREATE TABLE statement. Views are read-only.


6. DROP VIEW syntax
DROP VIEW table_name
Removes a view from the database. A view can be changed by dropping and recreating it.


7. CREATE SEQUENCE syntax
CREATE SEQUENCE name
[ INCRE
MENT increment_value ]
[ MINVALUE minimum_value ]
[ MAXVALUE maximum_value ]
[ START start_value ]
[ CACHE cache_value ]
[ CYCLE ]
Creates a new sequence generator that can be used to generate an iterative sequence of values. Sequence generators have a number of uses including the creation of primary keys for a table. The INCREMENT, MINVALUE, MAXVALUE, START, and CACHE values are all optional.
The INCREMENT value specifies how the sequence increments each iteration. By default a sequence generator increments by 1. The MINVALUE and MAXVALUE values specify the bounds of the sequence generator. By default MINVALUE and MAXVALUE are 0 and Long.MAX_VALUE respectively. The START value specifies the first key (exclusive) of the generator. The CACHE value specifies how many keys should be cached ahead of time.
Below is an example that creates a new sequence generator called ‘seq_key_1’ that starts at 10 and increments by 2 each iteration;
CREATE SEQUENCE seq_key_1 INCREMENT 2 START 10
A sequence generator is accessed by a call to the NEXTVAL function. TheNEXTVAL function iterates the generator and returns the next value from the sequence. The NEXTVAL function is an atomic operation and guarantees that no two identical values will be returned regardless of the frequency or concurrency of calls to the function. Below is a simple example;
SELECT NEXTVAL(‘seq_key_1’)

8. DROP SEQUENCE syntax

DROP SEQUENCE name
Drops a sequence generator previously created with the CREATE SEQUENCEstatement. A sequence generator may be changed by dropping the sequence and then recreating it.


9. COMPACT TABLE syntax
COMPACT TABLE table_name
Compacts the table data file in the file system. This removes all unused space from the table file and may rearrange the structure of the table to a form that better fits the characteristics of the data being stored.

10. CREATE SCHEMA syntax

CREATE SCHEMA schema_name
Creates a schema with the given name. By default a database has three schema initially defined, SYS_INFOSYS_JDBC and APP. The SYS_INFO and SYS_JDBCschema contain a number of important system tables and the APP schema is the default user schema.
The following is an example of creating a new schema and changing to it;
CREATE SCHEMA my_schema;
SET SCHEMA my_schema;

11. DROP SCHEMA syntax

DROP SCHEMA schema_name
Drops the schema with the given name. A schema may only be dropped if it contains no tables. The SYS_INFO and APP schema may not be dropped.


12. INSERT syntax
INSERT INTO table_name [ ( col_name1, col_name2, …. ) ]
VALUES ( expression1_1, expression1_2, …. ),
( expression2_1, expression2_2, …. ), ….
INSERT INTO table_name [ ( col_name1, col_name2, …. ) ]
SELECT …
INSERT INTO table_name
SET col_name1 = expression1, col_name2 = expression2, ….
This is the SQL command to insert records into a table in the database. This statement comes in three forms. The first inserts data from a VALUES clause;
INSERT INTO table ( col1, col2, col3 )
VALUES ( 10, 4 + 3, CONCAT(‘1’, ‘1’, ‘c’) ),
( 11, (28 / 2) – 7, CONCAT(col1, ‘c’) )
The second form is used to copy information from a SELECT query into the table specified in the INSERT statement. For example;
INSERT INTO table ( col1, col2, col3 )
SELECT id, num, description
FROM table2
WHERE description LIKE ‘11%’
The third form uses a list of column SET assignments. For example;
INSERT INTO table
SET col1 = 10, col2 = 4 + 3, col3 = CONCAT(col1, ‘c’)
If a column of the table is not specified in an INSERT the default value declared for the column is used. If no default value was declared a NULL value is inserted in the column. If the column is declared as NOT NULL the insert operation fails.


13. DELETE syntax
DELETE FROM table_name
[ WHERE expression ]
[ LIMIT limit_amount ]
Deletes all the rows from the table that match the WHERE clause. An optionalLIMIT clause specifies the maximum number of matched rows to be removed. An example of using the DELETE statement;
DELETE FROM table
WHERE col3 LIKE ‘11%’ AND col1 < 1000 LIMIT 200

14. UPDATE syntax

UPDATE table_name
SET col_name1 = expression1, col_name2 = expression2, ….
[ WHERE expression ]
[ LIMIT limit_amount ]
Updates information in a table. The SET clause is a list of assignments that describe how the columns of the data matched by the WHERE clause are to be updated. Any columns not assigned in the SET clause are left unchanged. Examples of using UPDATE;
UPDATE Employee
SET salary = salary * 1.25
WHERE name = ‘Bob’
UPDATE Order
SET id = id + 3, part = CONCAT(part, ‘-00’)
WHERE part LIKE ‘PO-%’
LIMIT 10


15. SELECT syntax
SELECT [ DISTINCT | ALL ]
column_expression1, column_expression2, ….
[ FROM from_clause ]
[ WHERE where_expression ]
[ GROUP BY expression1, expression2, …. ]
[ HAVING having_expression ]
[ ORDER BY order_column_expr1, order_column_expr2, …. ]
column_expression ::= expression [ AS ] [ column_alias ]
from_clause ::= select_table1, select_table2, …
from_clause ::= select_table1 LEFT [OUTER] JOIN select_table2 ON expr  …
from_clause ::= select_table1 RIGHT [OUTER] JOIN select_table2 ON expr  …
from_clause ::= select_table1 [INNER] JOIN select_table2  …
select_table ::= table_name [ AS ] [ table_alias ]
select_table ::= ( sub_select_statement ) [ AS ] [ table_alias ]
order_column_expr ::= expression [ ASC | DESC ]
The SELECT statement is used to form queries for extracting information out of the database. The following example query will return the number, quantity and price of all orders for more than 5 items sorted in descending order by order number. In addition it rounds the order price to two decimal places and applies a dollar ($) sign to the output.
SELECT number, quantity, CONCAT(‘$’, ROUND(price, 2))
FROM Order
WHERE quantity > 5
ORDER BY number DESC
The ORDER BY and GROUP BY clause may refer to a column, a column alias, or an expression. The HAVING clause is evaluated after the grouping and aggregate columns have been resolved.
For examples of using SELECT with aggregate functions see the ‘Internal SQL Functions’ section.

16. COMMIT and ROLLBACK syntax

COMMIT
ROLLBACK
Transactional operations for closing a transaction and either committing all the changes made or rolling back and disposing all changes. COMMIT may cause a concurrent transaction conflict exception to be thrown. If a conflict is detected the transaction is automatically rolled back. See the ‘Transactions’ section of the documentation for further details of how Mckoi handles transactions.


17. CREATE USER, ALTER USER and DROP USER syntax
CREATE USER username SET PASSWORD ‘password’
[ SET GROUPS groups_list ]
[ SET ACCOUNT ( LOCK | UNLOCK ) ]
ALTER USER username SET PASSWORD ‘password’
[ SET GROUPS groups_list ]
[ SET ACCOUNT ( LOCK | UNLOCK ) ]
DROP USER username
These are user management commands for creating/altering and dropping users in the system. Only members of the ‘secure access’ group are permitted to perform these operations, which includes the administrator user that is setup when the Mckoi database is created.
The following example creates a user called ‘harry’ with the password ‘cat’;
CREATE USER harry SET PASSWORD ‘cat’
See the ‘JDBC Driver’ section for documentation on connecting to a database using a username and password to connect to a database.


18. GRANT/REVOKE syntax
GRANT privileges ON database_object TO ( PUBLIC | user_list )
[ WITH GRANT OPTION ]
REVOKE [ GRANT OPTION FOR ] privileges ON database_object
FROM ( PUBLIC | user_list )
privileges ::= priv_item1, priv_item2, …
priv_item ::= ALL [ PRIVILEGES ] | SELECT | INSERT | UPDATE |
DELETE | REFERENCES | USAGE
database_object ::= [ TABLE ] table_name | SCHEMA schema_name
user_list ::= PUBLIC | username1, username2, …
Grants or revokes types of access on a table or view to a user. When a table or view is created the system gives full grant options to the user that created the object. The user is given the option to grant other users selective access to the object through the GRANT and REVOKE syntax. For example, the follow statement shows how a user would grant user ‘toby’ permission to SELECT from a table called MyTable;
GRANT SELECT ON TABLE MyTable TO toby
The GRANT command allows granting all users access to an object. The following statement makes MyTable globally readable;
GRANT SELECT ON TABLE MyTable TO PUBLIC
If you wish to give a user the option of granting a privilege to another user, addWITH GRANT OPTION to the GRANT statement.


19. SET syntax
SET variable = expression
SET AUTO COMMIT ( ON | OFF )
SET TRANSACTION ISOLATION LEVEL ( SERIALIZABLE )
SET SCHEMA schema_name
Makes a change to the state of the connection. SET AUTO COMMIT is used to switch transaction ‘auto commit mode’ on or off. When auto commit mode is on the engine commits after every statement. By default, a connection starts with auto commit mode switched on. SET TRANSACTION ISOLATION LEVEL currently only supports the SERIALIZABLE isolation level. See the ‘Transactions’ section of the documentation for details of how Mckoi handles transactions.
SET SCHEMA is used to change the default schema of a connection.

20. DESCRIBE syntax

DESCRIBE table_name
This command provides information about the columns of the table. It shows the column names, the type / size and scale (if applicable) and other useful information.

21. SHOW syntax

SHOW engine_variable
engine_variable ::= TABLES | SCHEMA | STATUS | CONNECTIONS
Shows internal information about the database system. SHOW TABLES returns a list of tables in the database. SHOW STATUS returns debugging and statistical information about the internal state of the database engine. SHOW CONNECTIONSreturns a snapshot of the current connections on the database. SHOW SCHEMAlists all the schema defined.

22. SHUTDOWN syntax

SHUTDOWN
Shuts down the database. If the database is running as a server the database shuts down cleanly and the process is stopped. If the database is embedded in a Java application it is cleanly put into a shut down state.
Only a user with the correct grants may successfully execute this command.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s