SQL INSERT Statements

Objectives

This lesson covers the following objectives:

• Explain the importance of being able to alter the data in a database
• Construct and execute INSERT statements which insert a single row using a VALUES clause
• Construct and execute SQL INSERT statements that use special values, null values, and date values
• Construct and execute INSERT statements that copy rows from one table to another using a subquery

Purpose of SQL INSERT Statements

• Up to now, you have been learning how to access data in a database.
• It’s time to learn how to make changes to the data in the database.
• In business, databases are dynamic.
• They are constantly in the process of having data inserted, updated, and deleted.
• Think how many times the school’s student database changes from day to day and year to year.
• Unless changes are made, the database would quickly lose its usefulness.
• In this lesson, you will begin to use data manipulation language (DML) statements to make changes to a database.

Copy Tables Before Inserting

• You will be responsible for altering tables in your schema.
• You will also be responsible for restoring them just as a real Database Administrator would assume that responsibility.
• To keep your schema tables in their original state, you will make a copy of each table before completing the practice activities in this and later lessons.
• In each practice activity, you will use the copy of the table that you create, not the original.
• If you inadvertently alter a table copy, you can use the original table to restore the copy.
• You should name each copied table: copy_tablename.
• The table copies will not inherit the associated primaryto-foreign-key integrity rules (relationship constraints) of the original tables.
• The column data types, however, are inherited in the copied tables.

Syntax to Create a Copy of a Table

• Create table syntax:

CREATE TABLE copy_tablename
AS (SELECT * FROM tablename);

• For example:

CREATE TABLE copy_employees
AS (SELECT * FROM employees);

CREATE TABLE copy_departments
AS (SELECT * FROM departments);

• To verify and view the copy of the table, use the following DESCRIBE and SELECT statements:

DESCRIBE copy_employees;

SELECT * FROM copy_employees;

DESCRIBE copy_departments;

SELECT * FROM copy_departments;

SQL INSERT Statement

• The INSERT statement is used to add a new row to a table. The statement requires 3 values:
  • the name of the table
  • the names of the columns in the table to populate
  • corresponding values for each column
• How can we INSERT the data below to create a new department in the copy_departments table?

• The syntax below uses INSERT to add a new department to the copy_departments table.
• This statement explicitly lists each column as it appears in the table.
• The values for each column are listed in the same order.
  • Note that number values are not enclosed in single quotation marks.

INSERT INTO copy_departments
(department_id, department_name, manager_id, location_id)
VALUES
(200,'Human Resources', 205, 1500);

• Another way to insert values in a table is to implicitly add them by omitting the column names.
• One precaution: the values for each column must match exactly the default order in which they appear in the table (as shown in a DESCRIBE statement), and a value must be provided for each column.

• The INSERT statement in this example was written without explicitly naming the columns.
• For clarity, however, it is best to use the column names in an INSERT clause.

INSERT INTO copy_departments
VALUES
(210,'Estate Management', 102, 1700);

Check The Table First

• Before inserting data into a table, you must check several table details.
• The DESCRIBE tablename statement will return a description of the table structure in the table summary chart.
• COPY_DEPARTMENTS TABLE SUMMARY:

Table Summary

• As shown in the example, the table summary provides information about each column in the table, such as:
  • the allowance of duplicate values
  • the type of data allowed
  • the amount of data allowed
  • the allowance of NULL values
• Notice where the “Data Type” column is a character data type the “Length” column specifies the maximum number of characters permitted.

• First_name has data type VARCHAR2, and Length 20, this means that up to 20 characters can be entered for this column.
• For Number data types the brackets specify the Precision and Scale.
• Precision is the total number of digits, and Scale is the number of digits to the right of the decimal place.

By the way, data types will be covered in more detail later in the course.

• The SALARY column allows numbers with a Precision of 8 and a Scale of 2.
• The maximum value allowed in this column is 999999.99.

Inserting Rows With Null Values

• The INSERT statement need not specify every column — the Nullable columns may be excluded.
• If every column that requires a value is assigned a value, the insert works.
• In our example, the EMAIL column is defined as a NOT NULL column.
• An implicit attempt to add values to the table as shown would generate an error.

INSERT INTO copy_employees
(employee_id, first_name, last_name, phone_number, hire_date,
job_id, salary)
VALUES
(302,'Grigorz','Polanski', '8586667641', '15-Jun-2017',
'IT_PROG',4200);

• An implicit insert will automatically insert a null value in columns that allow nulls.
• To explicitly add a null value to a column that allows nulls, use the NULL keyword in the VALUES list.
• To specify empty strings and/or missing dates, use empty single quotation marks (with no spaces between them like this ”) for the missing data.

INSERT INTO copy_employees
(employee_id, first_name, last_name, email, phone_number,
hire_date, job_id, salary)
VALUES
(302,'Grigorz','Polanski', 'gpolanski', '', '15-Jun-2017',
'IT_PROG',4200);

Inserting Special Values

• Special values such as SYSDATE and USER can be entered in the VALUES list of an INSERT statement.
• SYSDATE will put the current date and time in a column.
• USER will insert the current session’s username, which is OAE_PUBLIC_USER in Oracle Application Express.
• This example adds USER as the last name, and SYSDATE for hire date.

INSERT INTO copy_employees
(employee_id, first_name, last_name, email, phone_number, hire_date,
job_id, salary)
VALUES
(304,'Test',USER, 't_user', 4159982010, SYSDATE, 'ST_CLERK',2500);

Inserting Specific Date Values

• The default format model for date data types is DDMon-YYYY.
• With this date format, the default time of midnight (00:00:00) is also included.
• In an earlier section, we learned how to use the TO_CHAR function to convert a date to a character string when we want to retrieve and display a date value in a non-default format.
• Here is a reminder of TO_CHAR:

SELECT first_name, TO_CHAR(hire_date,'Month, fmdd, yyyy')
FROM employees
WHERE employee_id = 101;

• Similarly, if we want to INSERT a row with a non-default format for a date column, we must use the TO_DATE function to convert the date value (a character string) to a date.

A second example of TO_DATE allows the insertion of a specific time of day, overriding the default time of midnight.

SELECT first_name, last_name,
TO_CHAR(hire_date, 'dd-Mon-YYYY HH24:MI') As "Date and Time"
FROM copy_employees
WHERE employee_id = 303;

Using A Subquery To Copy Rows

• Each INSERT statement we have seen so far adds only one row to the table.
• But suppose we want to copy 100 rows from one table to another.
• We do not want to have to write and execute 100 separate INSERT statements, one after the other.
• That would be very time-consuming.
• Fortunately, SQL allows us to use a subquery within an INSERT statement.
• All the results from the subquery are inserted into the table.
• So we can copy 100 rows – or 1000 rows – with one multiple-row subquery within the INSERT.
• As you would expect, you don’t need a VALUES clause when using a subquery to copy rows because the inserted values will be exactly the values returned by the subquery.
• In the example shown, a new table called SALES_REPS is being populated with copies of some of the rows and columns from the EMPLOYEES table.
• The WHERE clause is selecting those employees that have job IDs like ‘%REP%’.

INSERT INTO sales_reps(id, name, salary, commission_pct)
SELECT employee_id, last_name, salary, commission_pct
FROM employees
WHERE job_id LIKE '%REP%';

• The number of columns and their data types in the column list of the INSERT clause must match the number of columns and their data types in the subquery.
• The subquery is not enclosed in parentheses as is done with the subqueries in the WHERE clause of a SELECT statement.
• If we want to copy all the data – all rows and all columns – the syntax is even simpler.
• To select all rows from the EMPLOYEES table and insert them into the SALES_REPS table, the statement would be written as shown:

INSERT INTO sales_reps
SELECT *
FROM employees;

• Again, this will work only if both tables have the same number of columns with matching data types, and they are in the same order.

Terminology of SQL INSERT Statements

Key terms used in this lesson included:

• INSERT INTO
• USER
• Transaction
• Explicit

Summary of SQL INSERT Statements

In this lesson, you should have learned how to:

• Explain the importance of being able to alter the data in a database
• Construct and execute SQL INSERT statements which insert a single row using a VALUES clause
• Construct and execute INSERT statements that use special values, null values, and date values
• Construct and execute SQL INSERT statements that copy rows from one table to another using a subquery