197 Column Data Types Of course, you should apply common sense to all this freedom. Just because you can call a database `create database`, it doesn’t that mean that you should.The same prin- ciple applies as in any other kind of programming—use meaningful identifiers. Column Data Types The three basic column types in MySQL are: numeric, date and time, and string.Within each of these categories are a large number of types.We’ll summarize them here, and go into more detail about the strengths and weaknesses of each in Chapter 11. Each of the three types comes in various storage sizes.When choosing a column type, the principle is generally to choose the smallest type that your data will fit into. For many data types, when you are creating a column of that type, you can specify the maximum display length.This is shown in the following tables of data types as M.If it’s optional for that type, it is shown in square brackets.The maximum value you can specify for M is 255. Optional values throughout these descriptions are shown in square brackets. Numeric Types The numeric types are either integers or floating point numbers. For the floating point numbers, you can specify the number of digits after the decimal place.This is shown in this book as D.The maximum value you can specify for D is 30 or M-2 (that is, the maxi- mum display length minus two—one character for a decimal point and one for the inte- gral part of the number), whichever is lower. For integer types you can also specify if you want them to be UNSIGNED, as shown in Listing 8.1. For all numeric types, you can also specify the ZEROFILL attribute.When values from a ZEROFILL column are displayed, they will be padded with leading zeroes. If you specify a column as ZEROFILL, it will automatically also be UNSIGNED. The integral types are shown in Table 8.5. Note that the ranges shown in this table show the signed range on one line and the unsigned range on the next. Table 8.5 Integral Data Types Type Range Storage Description (bytes) TINYINT[(M)] -127 128 1 Very small or 0 255 integers BIT Synonym for TINYINT BOOL Synonym for TINYINT SMALLINT[(M)] -32768 32767 2 Small integers or 0 65535 11 525x ch08 1/24/03 3:39 PM Page 197 198 Chapter 8 Creating Your Web Database MEDIUMINT[(M)] -8388608 3 Medium sized 8388607 integers or 0 16777215 INT[(M)] -2 31 2 31 -1 4 Regular integers or 0 2 32 -1 INTEGER[(M)] Synonym for INT BIGINT[(M)] -2 63 2 63 -1 8 Big integers or 0 2 64 -1 The floating point types are shown in Table 8.6. Table 8.6 Floating Point Data Types Type Range Storage Description (bytes) FLOAT(precision) depends on varies Can be used to specify precision single or double precision floating point numbers. FLOAT[(M,D)] ±1.175494351E-38 4 Single precision ±3.402823466E+38 floating point number. These are equivalent to FLOAT(4), but with a specified display width and number of decimal places. DOUBLE[(M,D)] ±1. 8 Double precision 7976931348623157E floating point number. +308 These are equivalent ±2.2250738585072014E to FLOAT(8) but with a -308 specified display width and number of decimal places. DOUBLE Synonym for PRECISION[(M,D)] as above DOUBLE[(M, D)]. REAL[(M,D)] as above Synonym for DOUBLE[(M, D)]. DECIMAL[(M[,D])] varies M+2 Floating point number stored as char.The range depends on M, the display width. NUMERIC[(M,D)] as above Synonym for DECIMAL. DEC[(M,D)] as above Synonym for DECIMAL. Table 8.5 Continued Type Range Storage Description (bytes) 11 525x ch08 1/24/03 3:39 PM Page 198 199 Column Data Types Date and Time Types MySQL supports a number of date and time types.These are shown in Table 8.7.With all these types, you can input data in either a string or numerical format. It is worth not- ing that a TIMESTAMP column in a particular row will be set to the date and time of the most recent operation on that row if you don’t set it manually.This is useful for transac- tion recording. Table 8.7 Date and Time Data Types Type Range Description DATE 1000-01-01 A date.Will be displayed as YYYY-MM-DD. 9999-12-31 TIME -838:59:59 A time.Will be displayed as HH:MM:SS.Note 838:59:59 that the range is much wider than you will probably ever want to use. DATETIME 1000-01-01 A date and time.Will be displayed as 00:00:00 YYYY-MM-DD HH:MM:SS. 9999-12-31 23:59:59 TIMESTAMP[(M)] 1970-01-01 A timestamp, useful for transaction reporting. 00:00:00 The display format depends on the value of M (see Table 8.8, which follows). Sometime The top of the range depends on the limit in 2037 on UNIX timestamps. YEAR[(2|4)] 70–69 A year.You can specify 2 or 4 digit format. (1970–2069) Each of these has a different range, 1901–2155 as shown. Table 8.8 shows the possible different display types for TIMESTAMP. Table 8.8 TIMESTAMP Display Types Type Specified Display TIMESTAMP YYYYMMDDHHMMSS TIMESTAMP(14) YYYYMMDDHHMMSS TIMESTAMP(12) YYMMDDHHMMSS TIMESTAMP(10) YYMMDDHHMM TIMESTAMP(8) YYYYMMDD TIMESTAMP(6) YYMMDD TIMESTAMP(4) YYMM TIMESTAMP(2) YY 11 525x ch08 1/24/03 3:39 PM Page 199 200 Chapter 8 Creating Your Web Database String Types String types fall into three groups. First, there are plain old strings, that is, short pieces of text.These are the CHAR (fixed length character) and VARCHAR (variable length character) types.You can specify the width of each. Columns of type CHAR will be padded with spaces to the maximum width regardless of the size of the data, whereas VARCHAR columns vary in width with the data. (Note that MySQL will strip the trailing spaces from CHARs when they are retrieved, and from VARCHARs when they are stored.) There is a space versus speed trade off with these two types, which we will discuss in more detail in Chapter 11. Second, there are TEXT and BLOB types.These come in various sizes.These are for longer text or binary data, respectively. BLOBs are binary large objects.These can hold any- thing you like, for example, image or sound data. In practice, BLOB and TEXT columns are the same except that TEXT is case sensitive and BLOB is not. Because these column types can hold large amounts of data, they require some special considerations.We will discuss this in Chapter 11. The third group has two special types, SET and ENUM.The SET type is used to specify that values in this column must come from a particular set of specified values. Column values can contain more than one value from the set.You can have a maximum of 64 things in the specified set. ENUM is an enumeration. It is very similar to SET, except that columns of this type can have only one of the specified values or NULL, and that you can have a maximum of 65,535 things in the enumeration. We ’ve summarized the string data types in Tables 8.9, 8.10, and 8.11.Table 8.9 shows the plain string types. Table 8.9 Regular String Types Type Range Description [NATIONAL] 0 to 255 Fixed length string of length M, where M is CHAR(M) [BINARY] characters between 0 and 255.The NATIONAL keyword spec- ifies that the default character set should be used. This is the default in MySQL anyway, but is included as it is part of the ANSI SQL standard. The BINARY keyword specifies that the data should be treated as not case insensitive. (The default is case sensitive.) CHAR 1 Synonym for CHAR(1) [NATIONAL] 1 to 255 Same as above, except they are variable length. VARCHAR(M) characters [BINARY] Table 8.10 shows the TEXT and BLOB types.The maximum length of a TEXT field in char- acters is the maximum size in bytes of files that could be stored in that field. 11 525x ch08 1/24/03 3:39 PM Page 200 201 Further Reading Table 8.10 TEXT and BLOB Types Type Maximum Length Description (characters) TINYBLOB 2 8 -1 A tiny binary large object (BLOB) field (that is, 255) TINYTEXT 2 8 -1 A tiny TEXT field (that is, 255) BLOB 2 16 -1 A normal sized BLOB field (that is, 65,535) TEXT 2 16 -1 A normal sized TEXT field (that is, 65,535) MEDIUMBLOB 2 24 -1 A medium sized BLOB field (that is, 16,777,215) MEDIUMTEXT 2 24 -1 A medium sized TEXT field (that is, 16,777,215) LONGBLOB 2 32 -1 A long BLOB field (that is, 4,294,967,295) LONGTEXT 2 32 -1 A long TEXT field (that is, 4,294,967,295) Table 8.11 shows the ENUM and SET types. Table 8.11 SET and ENUM Types Type Maximum Values in Set Description ENUM('value1', 65,535 Columns of this type can only 'value2', ) hold one of the values listed or NULL. SET('value1', 64 Columns of this type can hold 'value2', ) a set of the specified values or NULL. Further Reading For more information, you can read about setting up a database at the MySQL online manual at http://www.mysql.com/. 11 525x ch08 1/24/03 3:39 PM Page 201 . will probably ever want to use. DATETIME 100 0-0 1-0 1 A date and time.Will be displayed as 00:00:00 YYYY-MM-DD HH:MM:SS. 999 9-1 2-3 1 23:59:59 TIMESTAMP[(M)] 197 0-0 1-0 1 A timestamp, useful for transaction. recording. Table 8.7 Date and Time Data Types Type Range Description DATE 100 0-0 1-0 1 A date.Will be displayed as YYYY-MM-DD. 999 9-1 2-3 1 TIME -8 38:59:59 A time.Will be displayed as HH:MM:SS.Note 838:59:59 that. integers or 0 16777215 INT[(M)] -2 31 2 31 -1 4 Regular integers or 0 2 32 -1 INTEGER[(M)] Synonym for INT BIGINT[(M)] -2 63 2 63 -1 8 Big integers or 0 2 64 -1 The floating point types are