What is Sql: Definition and 77 Discussions

SQL ( (listen) S-Q-L, "sequel"; Structured Query Language) is a domain-specific language used in programming and designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS). It is particularly useful in handling structured data, i.e. data incorporating relations among entities and variables.
SQL offers two main advantages over older read–write APIs such as ISAM or VSAM. Firstly, it introduced the concept of accessing many records with one single command. Secondly, it eliminates the need to specify how to reach a record, e.g. with or without an index.
Originally based upon relational algebra and tuple relational calculus, SQL consists of many types of statements, which may be informally classed as sublanguages, commonly: a data query language (DQL), a data definition language (DDL), a data control language (DCL), and a data manipulation language (DML). The scope of SQL includes data query, data manipulation (insert, update and delete), data definition (schema creation and modification), and data access control. Although SQL is essentially a declarative language (4GL), it also includes procedural elements.
SQL was one of the first commercial languages to use Edgar F. Codd’s relational model. The model was described in his influential 1970 paper, "A Relational Model of Data for Large Shared Data Banks". Despite not entirely adhering to the relational model as described by Codd, it became the most widely used database language.SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987. Since then, the standard has been revised to include a larger set of features. Despite the existence of standards, most SQL code requires at least some changes before being ported to different database systems.

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  1. W

    SQL query for Records containing a Character

    Hi All, I am trying to do an SQL query for records containing a certain character, say, c , in 'field' I think if the character c is at the beginning, we use : Select ... from table where field like 'c % ' , where % is a wildcard. Similar for cases where the character is at the end, i.e., we...
  2. W

    SQL Queries using Null fields -- Must use "is null" or "is not null"?

    Hi all, This is for SQL queries, sorry ran out of space in the title. Say we are doing a query that includes a null field/attribute. Must we always use either an " Is null" or " Is not null" statement? Thanks.
  3. W

    Downloading Data for Access SQL

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  4. Nicosia1

    What is the Intersection of Computer Programming and Music in Nicosia?

    I am a computer programmer, mostly in Windows, but a little bit into open source, Linux and Java. I work a lot in javascript and SQL of one kind or another, both of which are utilized somehow via all common platforms. I am also interested in music, physics, and chemistry. I play piano and...
  5. W

    How to Modify Names in an SQL View?

    Does anyone know how to change names in an SQL view (i.e., a sort of a subset of a database. We may create it by saving a query and then doing a query on this saved query )? Thanks.
  6. W

    [SQL] Referential Integrity Details

    Hi a probably dumb question on Referential Integrity: I think I understand the basic idea/motivation for it, but one thing I am confused about is this: just when/how do we declare a column in a given table T' to be a foreign key related to the primary key for table T? Is it when we...
  7. W

    [SQL] Way of Relating any two Tables?

    Hi all, Say we have a collection T_1, T_2,..., T_n of tables. I would like for any pair to be related. Would it work if I where to select any field, say the primary key PKT_1 for T_1 and insert it (albeit artificially) meaning include it as an attribute in every other table? If we did this...
  8. W

    [SQL] Query using Data from 2 Tables

    Hi, say I am doing a query for which I need data from two tables, on, say the salary of those who teach French from 2-to-3 P.M, and one table T_1 contains the teaching subject and another table T_2 contains the class schedule/hours. Say these two tables are related. Do we then do a query...
  9. W

    [SQL] Order of Appearence in Query Results.

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  10. W

    Difference Between Sort By, Order By & Group By

    Hi, just curious about the difference between the " Sort By " and " Order By" commands in database. I assume Sort by is used in QBE and "Order by" is used in SQL ? While we're at it, how about "Group By"? Thanks.
  11. B

    How Should Manage Be Represented in an ER Diagram for a Video Rental Company?

    I am doing a ER Diagram for a class and having a lot of trouble with a specific piece of the sentence. Anyway, here is the business requirements we are diagramming: The video rental company has several branches throughout the USA. The data held on each branch is the branch address made up of...
  12. W

    SQL "Where not exists" (nested loops)

    I'm having a hard time understanding how nested loops work in SQL. Find all the people who likes all the hobbies. select p.name from person p where not exists (select * from (select distinct h.hobby from hobby h) as h1 where not exists (select *...
  13. N

    Oracle SQL Query: Employees Managers & Supervisors

    Hello, I have written the below queries, can somebody tell me if they are correct. manager_id in Employee Table - supervisor ; manager_id in departments table - manager. names and department names of managers who do not supervise any employee. select e.first_name|| ' ' ||e.last_name...
  14. J

    Can a Foreign Key Reference a Foreign Key?

    Hi I am trying to create the tables below and having problems with the timeLog table referencing allocation, when I put it into the modified form of Oricle my University uses it dosent like me refrencing the refrenced values it spits out the error: ORA-02256: number of referencing columns must...
  15. C

    SQL: Count No of Students Enrolled in Subjects

    Iam currently coding a database system for a school here, currently this is my database in MYSQL I want to know what SQL code to use to count how many students has enrolled in every subjects in the subjects table the new relation would appear as...
  16. M

    What the best online resource to learn about SQL injection attacks?

    Hallo all, I need a very conceptual and clear cut definition on sql attacks...there are so many forms of definition and material available on internet that I am just so confused...what the most reliable and authentic source to grasp this info. Thanks
  17. DaveC426913

    SQL JOIN Query for Retrieving Pics in Multiple Categories

    I've got 3 tables: Pics - table of my pictures Categories - table of categories that pictures will fall into PicsCategories - a many-to-many table relating pictures to categories. So the primary key of this table consists of a pic field and a category field So now I want to provide a...
  18. C

    Writing SQL Queries: Can You Have 2 Efficient Solutions?

    I just have a general question that I came up with while doing homework for my database class. I was asked to write a specific query, and when I checked my answer against the posted solutions, it was different. I don't know that much SQL (yet), but I'm pretty sure that my query would produce the...
  19. F

    Understanding SQL Relationships and How to Define Them in SQL Server

    I'm trying to learn SQL, specifically for SQL server. One question I have is about defining relationships. I know how to build a relationship graphically (showing that the primary key from one table is the foreign key of another), but I'm not sure how to assert the relationship with an...
  20. P

    Learn SQL Basics - A Guide for Beginners

    please tell me any site where i can study SQL basics. thnx
  21. P

    Boolean operators in SQL - Correct Syntax?

    Hi all, Trying to write an SQL query for the Sloan Digital Sky Survey that uses the NOT operator, and failing miserably. Basically, I'm making photometric cuts in 4-d colour space, and I currently have a selection of inequalities that select enclosed regions of colour space. However, I...
  22. R

    Find Common Elements in Lists: SQL Query or PHP Nested Loops?

    I get a list from a query. Let's say "SELECT name FROM foods WHERE type='fruit';" returns "apple, orange, banana" I get a list from another query, "SELECT name FROM concepts WHERE type='color';" returns "red, orange, yellow" Now what I want is to find the common element(s) in the two...
  23. R

    MySQL: Logging SQL Statements for Debugging PHP Apps

    Goal: I seek to log the SQL statements into a MySQL table, with the time they were executed as an aid to debugging problems with PHP apps I am writing. Problem: MySQL seems to try to interpret the statement, meant to simply be data in a field. When I try to "INSERT" the values, I get MySQL...
  24. K

    Help Joining Two Tables in SQL?

    I'm having trouble getting the following work. Can anyone help me? I have two tables that look like the following: Table 1 Table 2 A B A B C 1 4 1 4 6 2 5 3 6 How do I join both of them such...
  25. P

    Removing Columns After Table Creation Using SQL

    Isn't possible to delete and remove columns after a table has been created? Rows works just fine but columns don't...
  26. P

    How to Display a SQL Database as a Table in a Win32 Program?

    Let's say I'm communicating with a SQL (local) database using sqlite. How would i go about displaying this database as a table in a win32 program using either dev-c++ or MSVS++?
  27. Saint

    I want to learn about networking and SQL

    I want to learn about networking and SQL, where should i start? what books are good for this ? I want to learn the hardware and software knowledge on netwroking. Please suggest to me, thanks.
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