SQL For Dummies
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This Cheat Sheet consists of several helpful tables and lists, containing information that comes up repeatedly when working with structured query language (SQL). In one place, you can get a quick answer to a number of different questions that frequently arise during an SQL development effort.

SQL criteria for normal forms

To ensure that database tables are designed in such a way that they will hold your data reliably, you need to be sure that they are not subject to modification anomalies. Normalizing your databases will give you that assurance. Compare the SQL criteria in the following list to the tables in your database. Doing so will alert you to the possibility of anomalies, when you find that your database is not sufficiently normalized.

First Normal Form (1NF):

  • Table must be two-dimensional, with rows and columns.

  • Each row contains data that pertains to one thing or one portion of a thing.

  • Each column contains data for a single attribute of the thing being described.

  • Each cell (intersection of row and column) of the table must be single-valued.

  • All entries in a column must be of the same kind.

  • Each column must have a unique name.

  • No two rows may be identical.

  • The order of the columns and of the rows does not matter.

Second Normal Form (2NF):

  • Table must be in first normal form (1NF).

  • All non-key attributes (columns) must be dependent on the entire key.

Third Normal Form (3NF):

  • Table must be in second normal form (2NF).

  • Table has no transitive dependencies.

Domain-Key Normal Form (DK/NF):

  • Every constraint on the table is a logical consequence of the definition of keys and domains.

SQL data types

Here’s a list of all the formal data types that ISO/IEC standard SQL recognizes. In addition to these, you may define additional data types that are derived from these.

Exact Numerics:

  • INTEGER

  • SMALLINT

  • BIGINT

  • NUMERIC

  • DECIMAL

Approximate Numerics:

  • REAL

  • DOUBLE PRECISION

  • FLOAT

  • DECFLOAT

Binary Strings:

  • BINARY

  • BINARY VARYING

  • BINARY LARGE OBJECT

Boolean:

  • BOOLEAN

Character Strings:

  • CHARACTER

  • CHARACTER VARYING (VARCHAR)

  • CHARACTER LARGE OBJECT

  • NATIONAL CHARACTER

  • NATIONAL CHARACTER VARYING

  • NATIONAL CHARACTER LARGE OBJECT

Datetimes:

  • DATE

  • TIME WITHOUT TIMEZONE

  • TIMESTAMP WITHOUT TIMEZONE

  • TIME WITH TIMEZONE

  • TIMESTAMP WITH TIMEZONE

Intervals:

  • INTERVAL DAY

  • INTERVAL YEAR

Collection Types:

  • ARRAY

  • MULTISET

Other Types:

  • ROW

  • XML

SQL value functions

These SQL value functions perform operations on data. There are all kinds of operations that could conceivably be performed on data items, but these are some that are needed most often.

String Value Functions
Function Effect
SUBSTRING Extracts a substring from a source string
SUBSTRING SIMILAR Extracts a substring from a source string, using POSIX-based
regular expressions
SUBSTRING_REGEX Extracts from a string the first occurrence of an XQuery
regular expression pattern and returns one occurrence of the
matching substring
TRANSLATE_REGEX Extracts from a string the first or every occurrence of an
XQuery regular expression pattern and replaces it or them with an XQuery replacement string
UPPER Converts a character string to all uppercase
LOWER Converts a character string to all lowercase
TRIM Trims off leading or trailing blanks
TRANSLATE Transforms a source string from one character set to
another
CONVERT Transforms a source string from one character set to
another
Numeric Value Functions
Function Effect
POSITION Returns the starting position of a target string within a
source string
CHARACTER_LENGTH Returns the number of characters in a string
OCTET_LENGTH Returns the number of octets (bytes) in a character string
EXTRACT Extracts a single field from a datetime or interval
Datetime Value Functions
Function Effect
CURRENT_DATE Returns the current date
CURRENT_TIME(p) Returns the current time; (p) is precision of seconds
CURRENT_TIMESTAMP(p) Returns the current date and the current time; (p) is precision of seconds

SQL set functions

The SQL set functions give you a quick answer to questions you may have about the characteristics of your data as a whole. How many rows does a table have? What is the highest value in the table? What is the lowest? These are the kinds of questions that the SQL set functions can answer for you.

Function Effect
COUNT Returns the number of rows in the specified table
MAX Returns the maximum value that occurs in the specified able
MIN Returns the minimum value that occurs in the specified table
SUM Adds up the values in a specified column
AVG Returns the average of all the values in the specified column
LISTAGG Transforms values from a group of rows into a delimited string

Trigonometric and Logarithmic Functions

sin, cos, tan, asin, acos, atan, sinh, cosh, tanh, log(<base>, <value>), log10(<value>). ln( <value>)

JSON Constructor Functions

JSON_OBJECT

JSON_ARRAY

JSON_OBJECTAGG

JSON_ARRAYAGG

JSON Query Functions

JSON_EXISTS

JSON_VALUE

JSON_QUERY

JSON_TABLE

Knowing the MySQL WHERE clause format

The WHERE clause is used to modify a DELETE, SELECT, or UPDATE SQL query. This list shows the format you can use when writing a WHERE clause:

WHERE exp AND|OR exp AND|OR exp…

where exp can be one of the following:

column = value
column > value
column >= value
column < value
column <= value
column BETWEEN value1 AND value2
column IN (value1,value2,…)
column NOT IN (value1,value2,…)
column LIKE value
column NOT LIKE value

About This Article

This article is from the book:

About the book author:

Allen G. Taylor is a 30-year veteran of the computer industry and the author of over 40 books, including SQL For Dummies and Crystal Reports For Dummies. He lectures nationally on databases, innovation, and entrepreneurship. He also teaches database development internationally through a leading online education provider.

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