Database-MySQL [3i Infotech Placement]: Sample Questions 33 - 34 of 162
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Question 33
Explanation
- To retrieve information using SQL, SELECT is the 1st word is in query
SQL SELECT statement:
- Starts with the SELECT keyword
- Used to retrieve information from MySQL database tables.
- Made of several different keywords known as clauses.
- Query may retrieve information from specified columns or from all of the columns in the table.
- To specify the column name and the table name, to create a simple SQL SELECT statement
- The whole query is called SQL SELECT Statement.
Syntax of SQL SELECT Statement:
SELECT “column1”
[, “column2” , etc]
From “tablename”
[where “condition” ] ;
[] = optional
Conditional selections used in the where clause:
= Equal
> Greater
< Less than
>= Greater than or equal
<= Less than or equal
<> Not equal to
Ex .
SELECT first_name + ‘’ +
Last_name As emp_name FROM
Employee;
O/P
emp_name
Question 34
Explanation
Below the types of joins
- Inner Join
- Outer join
- Left outer join
- Right outer join
- Full join
- Inner join
The INNER JOIN keyword selects records that have matching values in both tables.
Syntax of Inner join
SELECT column_name (s)
FROM table1
INNER JOIN table2 ON table1. column_name = table2. column_name;
- Outer Join
Left Outer join:
- The left outer join keyword returns all records from the left table (table1) , and the matched records from the right table (table2) .
- The result is NULL from the right side, if there is no match.
Syntax of left outer join
SELECT column_name (s)
FROM table1
LEFT JOIN table2 ON table1. column_name = table2. column_name;
Right Outer join:
- The right outer join keyword returns all records from the right table (table2) , and the matched records from the left table (table1) .
- The result is NULL from the left side, when there is no match.
Syntax of right outer join:
SELECT column_name (s)
FROM table1
RIGHT JOIN table2 ON table1. column_name = table2. column_name;
Full Outer join:
- The FULL OUTER JOIN keyword return all records when there is a match in either left (table1) or right (table2) table records.
Full outer join syntax:
SELECT column_name (s)
FROM table1
FULL OUTER JOIN table2 ON table1. column_name = table2. column_name;
- Simple outer join is combination of left and right outerjoins.
- Apart from these there are
- Natural join: Cartisian product
- Equi join: Which includes = operator in condition
- NonEqui join: All conditional joins which do not use = in there conditions.