SQL complete solution

SQL What is SQL? ans: SQL stands for Structured Query Language. SQL lets you access and manipulate databases. What can SQL do? ans: SQL can execute queries against a database SQL can retrieve data from a database SQL can insert records in a database SQL can update records in a database SQL can delete records from a database SQL can create new databases SQL can create new tables in a database SQL can create stored procedures in a database SQL can create views in a database SQL can set permissions on tables, procedures, and views What is RDBMS and what are some examples? ans: RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access. The data in RDBMS is stored in database objects called tables. A table is a collection of related data entries and it consists of columns and rows. Are SQL queries case sensitive? ans: SQL keywords are NOT case sensitive: select is the same as SELECT What goes at the end of each SQL statement? ans: Some database systems require a semicolon at the end of each SQL statement. Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server. What is CRUD? ans: Create, Read/Retrieve (Select), Update and Delete are the four basic functions of persistent storage. SELECT Statement ans: The SELECT statement is used to select data from a database. Syntax: SELECT column_name, column_name FROM table_name; SELECT * FROM table_name; DISTINCT Statement ans: In a table, a column may contain many duplicate values; and sometimes you only want to list the different (distinct) values. Syntax: SELECT DISTINCT column_name,column_name FROM table_name; WHERE Clause ans: The WHERE clause is used to extract only those records that fulfill a specified criterion. Syntax: SELECT column_name,column_name FROM table_name WHERE column_name operator value; AND/OR Operators ans: The AND & OR operators are used to filter records based on more than one condition. Syntax: SELECT * FROM Customers WHERE Country='Germany' AND (City='Berlin' OR City='München'); ORDER BY Keyword ans: The ORDER BY keyword is used to sort the result-set by one or more columns. The ORDER BY keyword sorts the records in ascending order by default. To sort the records in a descending order, you can use the DESC keyword. SELECT column_name, column_name FROM table_name ORDER BY column_name ASC|DESC, column_name ASC|DESC; INSERT INTO Statement ans: The INSERT INTO statement is used to insert new records in a table. INSERT INTO table_name VALUES (value1,value2,value3,...); INSERT INTO table_name (column1,column2,column3,...) VALUES (value1,value2,value3,...); UPDATE Statement ans: The UPDATE statement is used to update existing records in a table. UPDATE table_name SET column1=value1,column2=value2,... WHERE some_column=some_value; Notice the WHERE clause in the SQL UPDATE statement! The WHERE clause specifies which record or records that should be updated. If you omit the WHERE clause, all records will be updated! DELETE Statement ans: The DELETE statement is used to delete rows in a table. DELETE FROM table_name WHERE some_column=some_value; Notice the WHERE clause in the SQL DELETE statement! The WHERE clause specifies which record or records that should be deleted. If you omit the WHERE clause, all records will be deleted! SELECT TOP Clause ans: The SELECT TOP clause is used to specify the number of records to return. The SELECT TOP clause can be very useful on large tables with thousands of records. Returning a large number of records can impact on performance. Note: Not all database systems support the SELECT TOP clause. SELECT TOP number|percent column_name(s) FROM table_name; LIKE Operator ans: The LIKE operator is used to search for a specified pattern in a column. SELECT column_name(s) FROM table_name WHERE column_name LIKE pattern; SELECT * FROM Customers WHERE City LIKE 's%'; IN Clause ans: The IN operator allows you to specify multiple values in a WHERE clause. SELECT column_name(s) FROM table_name WHERE column_name IN (value1,value2,...); SELECT * FROM Customers WHERE City IN ('Paris','London'); BETWEEN operator ans: The BETWEEN operator selects values within a range. The values can be numbers, text, or dates. SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2; Aliases (AS) ans: SQL aliases are used to give a database table, or a column in a table, a temporary name. Basically, aliases are created to make column names more readable. SELECT column_name AS alias_name FROM table_name; SELECT column_name(s) FROM table_name AS alias_name; JOIN ans: An SQL JOIN clause is used to combine rows from two or more tables, based on a common field between them. INNER JOIN ans: The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns in both tables. SELECT column_name(s) FROM table1 INNER JOIN table2 ON n_name=n_name; SELECT column_name(s) FROM table1 JOIN table2 ON n_name=n_name; LEFT JOIN ans: The LEFT JOIN keyword returns all rows from the left table (table1), with the matching rows in the right table (table2). The result is NULL in the right side when there is no match. SELECT column_name(s) FROM table1 LEFT JOIN table2 ON n_name=n_name; RIGHT JOIN ans: The RIGHT JOIN keyword returns all rows from the right table (table2), with the matching rows in the left table (table1). The result is NULL in the left side when there is no match. SELECT column_name(s) FROM table1 RIGHT JOIN table2 ON n_name=n_name; FULL OUTER JOIN ans: The FULL OUTER JOIN keyword returns all rows from the left table (table1) and from the right table (table2). The FULL OUTER JOIN keyword combines the result of both LEFT and RIGHT joins. SELECT column_name(s) FROM table1 FULL OUTER JOIN table2 ON n_name=n_name; UNION ans: The UNION operator is used to combine the result-set of two or more SELECT statements. Notice that each SELECT statement within the UNION must have the same number of columns. The columns must also have similar data types. Also, the columns in each SELECT statement must be in the same order. SELECT column_name(s) FROM table1 UNION SELECT column_name(s) FROM table2; SELECT INTO ans: The SELECT INTO statement selects data from one table and inserts it into a new table. SELECT * INTO newtable [IN externaldb] FROM table1; SELECT column_name(s) INTO newtable [IN externaldb] FROM table1; INSERT INTO ans: The INSERT INTO SELECT statement selects data from one table and inserts it into an existing table. Any existing rows in the target table are unaffected. INSERT INTO table2 SELECT * FROM table1; INSERT INTO table2 (column_name(s)) SELECT column_name(s) FROM table1; CREATE DATABASE ans: The CREATE DATABASE statement is used to create a database. CREATE DATABASE dbname; CREATE TABLE ans: The CREATE TABLE statement is used to create a table in a database. Tables are organized into rows and columns; and each table must have a name. CREATE TABLE table_name ( column_name1 data_type(size), column_name2 data_type(size), column_name3 data_type(size), .... ); SQL constraints ans: SQL constraints are used to specify rules for the data in a table. If there is any violation between the constraint and the data action, the action is aborted by the constraint. Constraints can be specified when the table is created (inside the CREATE TABLE statement) or after the table is created (inside the ALTER TABLE statement). CREATE TABLE table_name ( column_name1 data_type(size) constraint_name, column_name2 data_type(size) constraint_name, column_name3 data_type(size) constraint_name, .... ); NOT NULL Constraint ans: The NOT NULL constraint enforces a column to NOT accept NULL values. The NOT NULL constraint enforces a field to always contain a value. This means that you cannot insert a new record, or update a record without adding a value to this field. CREATE TABLE PersonsNotNull ( P_Id int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255) ) UNIQUE Constraint ans: The UNIQUE constraint uniquely identifies each record in a database table. The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint defined on it. Note that you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table. CREATE TABLE Persons ( P_Id int NOT NULL UNIQUE, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255) ) PRIMARY KEY ans: The PRIMARY KEY constraint uniquely identifies each record in a database table. Primary keys must contain UNIQUE values. A primary key column cannot contain NULL values. Most tables should have a primary key, and each table can have only ONE primary key. CREATE TABLE Persons ( P_Id int NOT NULL PRIMARY KEY, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255) ) FOREIGN KEY ans: A FOREIGN KEY in one table points to a PRIMARY KEY in another table. CREATE TABLE Orders ( O_Id int NOT NULL, OrderNo int NOT NULL, P_Id int, PRIMARY KEY (O_Id), FOREIGN KEY (P_Id) REFERENCES Persons(P_Id) ) CHECK Constraint ans: The CHECK constraint is used to limit the value range that can be placed in a column. If you define a CHECK constraint on a single column it allows only certain values for this column. If you define a CHECK constraint on a table it can limit the values in certain columns based on values in other columns in the row. CREATE TABLE Persons ( P_Id int NOT NULL CHECK (P_Id0), LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255) ) DEFAULT Constraint ans: The DEFAULT constraint is used to insert a default value into a column. The default value will be added to all new records, if no other value is specified. CREATE TABLE Persons ( P_Id int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Address varchar(255), City varchar(255) DEFAULT 'Sandnes' ); INDEX ans: The CREATE INDEX statement is used to create indexes in tables. Indexes allow the database application to find data fast; without reading the whole table. Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update). So you should only create indexes on columns (and tables) that will be frequently searched against. CREATE INDEX index_name ON table_name (column_name) DROP ans: Indexes, tables, and databases can easily be deleted/removed with the DROP statement. DROP INDEX table__name DROP DATABASE database_name ALTER ans: The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. To add a column in a table, use the following syntax: ALTER TABLE table_name ADD column_name datatype ALTER TABLE table_name DROP COLUMN column_name