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Structured Query Language


SQL is language of query standard for the DBMS. SQL taken as standard since year 1992. Initially applied at big DBMS like Oracle and of Informix, by now at DBMS base on PC like and dBASE of Foxpro. SQL have the character of as high level language. User only mentioning result of which is wanted and optimize execution of query conducted by DBMS. Language of SQL divided in two big shares, that is : DDL (Data of Definition Language) and DML (Data of Manipulation Language). DDL define data bases structure, like making of data bases, making of its tables. Example : CREATE DATABASE and of CREATE TABLE. DML represent shares for the manipulation of data bases like : data access, abolition, addition and distorting of data. DML also can be used to conduct data computing. Example : INSERT, DELETE, and UPDATE. SQL is relied on operations gathering of relational which have modify and repair.

Elementary structure of SQL consist of three clause, that is SELECT, FROM, and WHERE. SELECT have correspondence to with operation of projection at algebra relational. SELECT used to present attribute list at result of query. FROM have correspondence to with operation of Cartesian product at algebra relational. FROM used as by list an relationship table to process and in evaluation. WHERE have correspondence to with operation of selection at algebra relational. WHERE consist of predicate covering attribute in relationship which emerge at clause of FROM. Clause of WHERE used to determine criterion or predicate which must in fulfilling an relationship as result of query. This clause have the character of optionally, that is can use clause of WHERE or do not. Otherwise use clause of WHERE, hence query conducted by for all tuples at tables of which is mentioned at clause of FROM. Predicate at clause of WHERE can be combined with other relationship operator, like <, <=, >, >=, <> and logic operator, like AND, OR, NOT. Clause of WHERE can be used to conduct query with predicate which in form of an certain value range, that is by enhancing clause of BETWEEN. For attribute which is have type to of string can be conducted by an seeking with certain pattern, that is by exploiting character ‘%’ or ‘_’ (underscore) and enhance clause of LIKE at clause of WHERE ‘%’ for all substring ‘_’ for all appropriate character on course. Clause FROM used to determine tables to be made as source for the seeking of data In conducting query do not only limited to one tables, but is frequently required for relationship some tables at the same time. To present result of query pursuant to certain attribute sequence, hence can be conducted by enhancing clause ORDER BY, given by default is clause ORDER BY is sequence by menial (ASC), but to change to become sequence by is downhill, can be conducted by enhancing clause of DESC after name of attribute.
Functions of aggregation SQL :
• AVG : to get average value an attribute which is have type numeric.
• MIN : to get smallest value an attribute which is have type numeric.
• MAX : to get biggest value an attribute which is have type numeric.
• SUM : to get total value an attribute which is have type numeric.
• COUNT : to get value to the number of tuples.
Value NULL at one particular query can be treated peculiarly, that is earning is also treated for query to use expression of SQL. Manipulation data operations consist of addition of new tuple, distorting of attribute value, and abolition of tuple at one particular tables.
Command of SQL for the definition of data :
• CREATE : to form data bases, index or table.
• ALTER : to alter structure of table.
• DROP : to vanish data bases, index or table.
For the domain of data type cover as follows :
• Char(n) : type of String with length remain to equal to character n (if filled in character length less than n, hence the rest in content with space).
• Varchar(n) : type of String with flexible length, but maximal counted character n.
• Integer or int : integer type 2 byte.
• Smallint : type Integer 1 byte.
• Real, double, precision : type fraction of point floating decimal.
• Float(n) : type fraction of point floating decimal with digit n precision.
• Date : Type of is date of (composing 4 year digit of month, moon, and date).
• Time : time type (consisted of hour, minute, and second).
If an tables have index compositely (alliance), hence conducted by writing down all attribute at clause PRIMARY KEY.

SQL is language of query standard for the DBMS. SQL taken as standard since year 1992. Initially applied at big DBMS like Oracle and of Informix, by now at DBMS base on PC like and dBASE of Foxpro. SQL have the character of as high level language. User only mentioning result of which is wanted and optimize execution of query conducted by DBMS. Language of SQL divided in two big shares, that is : DDL (Data of Definition Language) and DML (Data of Manipulation Language). DDL define data bases structure, like making of data bases, making of its tables. Example : CREATE DATABASE and of CREATE TABLE. DML represent shares for the manipulation of data bases like : data access, abolition, addition and distorting of data. DML also can be used to conduct data computing. Example : INSERT, DELETE, and UPDATE. SQL is relied on operations gathering of relational which have modify and repair.

Elementary structure of SQL consist of three clause, that is SELECT, FROM, and WHERE. SELECT have correspondence to with operation of projection at algebra relational. SELECT used to present attribute list at result of query. FROM have correspondence to with operation of Cartesian product at algebra relational. FROM used as by list an relationship table to process and in evaluation. WHERE have correspondence to with operation of selection at algebra relational. WHERE consist of predicate covering attribute in relationship which emerge at clause of FROM. Clause of WHERE used to determine criterion or predicate which must in fulfilling an relationship as result of query. This clause have the character of optionally, that is can use clause of WHERE or do not. Otherwise use clause of WHERE, hence query conducted by for all tuples at tables of which is mentioned at clause of FROM. Predicate at clause of WHERE can be combined with other relationship operator, like <, <=, >, >=, <> and logic operator, like AND, OR, NOT. Clause of WHERE can be used to conduct query with predicate which in form of an certain value range, that is by enhancing clause of BETWEEN. For attribute which is have type to of string can be conducted by an seeking with certain pattern, that is by exploiting character ‘%’ or ‘_’ (underscore) and enhance clause of LIKE at clause of WHERE ‘%’ for all substring ‘_’ for all appropriate character on course. Clause FROM used to determine tables to be made as source for the seeking of data In conducting query do not only limited to one tables, but is frequently required for relationship some tables at the same time. To present result of query pursuant to certain attribute sequence, hence can be conducted by enhancing clause ORDER BY, given by default is clause ORDER BY is sequence by menial (ASC), but to change to become sequence by is downhill, can be conducted by enhancing clause of DESC after name of attribute.
Functions of aggregation SQL :
• AVG : to get average value an attribute which is have type numeric.
• MIN : to get smallest value an attribute which is have type numeric.
• MAX : to get biggest value an attribute which is have type numeric.
• SUM : to get total value an attribute which is have type numeric.
• COUNT : to get value to the number of tuples.
Value NULL at one particular query can be treated peculiarly, that is earning is also treated for query to use expression of SQL. Manipulation data operations consist of addition of new tuple, distorting of attribute value, and abolition of tuple at one particular tables.
Command of SQL for the definition of data :
• CREATE : to form data bases, index or table.
• ALTER : to alter structure of table.
• DROP : to vanish data bases, index or table.
For the domain of data type cover as follows :
• Char(n) : type of String with length remain to equal to character n (if filled in character length less than n, hence the rest in content with space).
• Varchar(n) : type of String with flexible length, but maximal counted character n.
• Integer or int : integer type 2 byte.
• Smallint : type Integer 1 byte.
• Real, double, precision : type fraction of point floating decimal.
• Float(n) : type fraction of point floating decimal with digit n precision.
• Date : Type of is date of (composing 4 year digit of month, moon, and date).
• Time : time type (consisted of hour, minute, and second).
If an tables have index compositely (alliance), hence conducted by writing down all attribute at clause PRIMARY KEY.

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