Unit2 Flashcards
SQL requires the use of the ______ command to enter data into a table.
Insert
Thus far, you have entered rows in which all of the attribute values are specified. But what do you do if a column does not have any available data? In those cases, you would want to leave the column with a valuer of null.
Inserting Rows with Null Attributes
There might be occasions when more than one attribute is optional. Rather than declaring each attribute as NULL in the INSERT command, you can indicate just the attributes that have required values. You do that by listing the attribute names inside parentheses after the table name.
Inserting Rows with Optional Attributes
The ______ command is used to list the contents of a table.
Select statements
list all attributes. A wildcard character is a symbol that can be used as a general substitute for other characters or commands.
*
Use the _____ command to modify data in a table.
Update statements
It is easy to delete a table row using the _____;
Delete statements
To add multiple rows to a table, using another table as the source of the data.
Inserting Rows from another table
Selecting Rows with Conditional Restrictions
Select Queries
SQL accepts any valid expressions (or formulas) in the computed columns. Such formulas can contain any valid mathematical operators and functions that are applied to attributes in any of the tables specified in the FROM clause of the SELECT statement.
Computed Columns
An alias is an alternative name given to a column or table in any SQL statement
Aliases
is a function that returns the current system date in sql server
getdate()
is a TSQL function that add a particular date interval from a given column or value. Its accepts the following parameters
dateadd()
is a function that returns the current system date in mysql
curdate()
is a MySQL function that subtracts a particular date interval from a given column or value. Its accepts the following parameters
date_sub
if both conditions are true
AND
if at least one of the condition is true
OR
if we want to negate the result of a conditional expression.
NOT
standard SQL allows the use of special operators in conjunction with the WHERE clause.
ANSI
Used to check whether an attribute value is within a range
BETWEEN
Used to check whether an attribute value is null
IS NULL
Used to check whether an attribute value matches a given string pattern
LIKE
Used to check whether an attribute value matches any value within a value list
IN
Used to check whether a subquery returns any rows
EXISTS
________ may be used to check whether an attribute value is within a range of values
BETWEEN
——- to check for a null attribute value
IS NULL
The _____ special operator is used in conjunction with wildcards to find patterns within string attributes.
LIKE
means any and all following or preceding characters are eligible
%
means any single character may be substituted for the underscore.
_
means any single character within a range or a set.
[]
means any single character NOT within a range or a set.
[^]
means any single character within a range or a set.
REGEXP []
means any single character NOT within a range or a set
REGEXP [^]
Many queries that would require the use of the logical OR can be more easily handled with the help of the special operator IN.
IN
The _____ special operator can be used whenever there is a requirement to execute a command based on the result of another query.
EXISTS
