ORACLE FROM
Oracle FROM clause is used with the Oracle SELECT statement and has a mandatory existence, as it is used to specify the tables from which the desired data needs to be retrieved.
Syntax: To select all fields from a table.
SELECT * FROM table_name;
Parameters:
table_name: It is used to specify the name of the table from which you want to retrieve the records.
Example: Selecting all fields from a table.
Students table:
STUDENT_ID STUDENT_NAME STUDENT_AGE 1 Joy 5 2 Smiley 13 3 Happy 11
Query:
SELECT * FROM students; |
Output:
ID NAME AGE 1 Joy 5 2 Smiley 13 3 Happy 11 3 rows returned in 0.02 seconds
Explanation:
The ‘students’ is an already existing table. Here we are selecting all the fields of the ‘students’ table and thus the record will be retrieved as it is.
Syntax: To select specific fields from a table.
SELECT expressions FROM table_name WHERE conditions;
Parameters:
expressions: It is used to specify the columns or calculations to be retrieved.
table_name: It is used to specify the name of the table from which you want to retrieve the records.
conditions: It is used to specify the conditions to be strictly followed for selection.
Example: Selecting specific fields from a table.
Students table:
STUDENT_ID STUDENT_NAME STUDENT_AGE 1 Joy 5 2 Smiley 13 3 Happy 11
Query:
SELECT name, age FROM students WHERE age > 10 ORDER BY name; |
Output:
ID NAME AGE 3 Happy 11 2 Smiley 13 2 rows returned in 0.01 seconds
Explanation:
The ‘students’ is an already existing table. Here we are selecting the specific fields ‘name’ and ‘age’ from the ‘students’ table with a condition that the selected row must have an age greater than 10. The ORDER BY clause defines the order in which the data needs to be displayed after retrieval. Here we are asking to order it by name.
Syntax: To select specific fields from multiple tables.
SELECT expressions FROM table1 INNER JOIN table2 ON join_predicate;
Parameters:
expressions: It is used to specify the columns or calculations to be retrieved.
table1: It is used to specify the name of the first table from which you want to retrieve the records.
table2: It is used to specify the name of the second table from which you want to retrieve the records.
join_predicate: It is used to specify the condition for joining tables.
Example: Selecting specific fields from multiple tables.
Students table:
STUDENT_ID STUDENT_NAME STUDENT_AGE 1 Joy 5 2 Smiley 13 3 Happy 11
Query:
SELECT students.name, teachers.subject FROM students INNER JOIN teachers ON students.student_id = student_id ORDER BY name; |
Output:
NAME SUBJECT Happy English Happy Hindi Joy English Joy Hindi Smiley English Smiley Hindi 6 rows returned in 0.03 seconds