The previous chapter discussed how to create tables and other
structures to hold your data. Now it is time to fill the tables
with data. This chapter covers how to insert, update, and delete
table data. We will also introduce ways to effect automatic data changes
when certain events occur: triggers and rewrite rules. The chapter
after this will finally explain how to extract your long-lost data
back out of the database.
When a table is created, it contains no data. The first thing to
do before a database can be of much use is to insert data. Data is
conceptually inserted one row at a time. Of course you can also
insert more than one row, but there is no way to insert less than
one row at a time. Even if you know only some column values, a
complete row must be created.
To create a new row, use the INSERT command.
The command requires the table name and a value for each of the
columns of the table. For example, consider the emp table
from Chapter 4:
CREATE TABLE emp (
empno NUMBER(4) NOT NULL CONSTRAINT emp_pk PRIMARY KEY,
ename VARCHAR2(10),
job VARCHAR2(9),
mgr NUMBER(4),
hiredate DATE,
sal NUMBER(7,2) CONSTRAINT emp_sal_ck CHECK (sal > 0),
comm NUMBER(7,2),
deptno NUMBER(2) CONSTRAINT emp_ref_dept_fk
REFERENCES dept(deptno)
);
An example command to insert a row would be:
INSERT INTO emp VALUES (7369,'SMITH','CLERK',7902,'17-DEC-80',800,NULL,20);
The data values are listed in the order in which the columns appear
in the table, separated by commas. Usually, the data values will
be literals (constants), but scalar expressions are also allowed.
The above syntax has the drawback that you need to know the order
of the columns in the table. To avoid that you can also list the
columns explicitly. For example, both of the following commands
have the same effect as the one above:
INSERT INTO emp (empno, ename, job, mgr, hiredate, sal, deptno)
VALUES (7369,'SMITH','CLERK',7902,'17-DEC-80',800,20);
INSERT INTO emp (ename, empno, mgr, job, sal, comm, deptno, hiredate)
VALUES('SMITH',7369,7902,'CLERK',800,NULL,20,'17-DEC-80');
Many users consider it good practice to always list the column
names.
If you don't have values for all the columns, you can omit some of
them. In that case, the columns will be filled with their default
values.
For clarity, you can also request default values explicitly, for
individual columns or for the entire row given that none of the
default values for any of the columns in that table have a not null
constraints on them.
INSERT INTO emp (ename, empno, mgr, job, sal, comm, deptno, hiredate)
VALUES('SMITH',7369,7902,'CLERK',800,DEFAULT,20,'17-DEC-80');
Tip: To do "bulk loads", that is, inserting a lot of data,
take a look at the COPY command. It is not as flexible as the
INSERT command, but is more efficient.