Common SQL Data types |
Numeric data typesMost commonly used numeric data types include: integer or INT - normal integer can be signed or unsigned. This is some times used just as INT when defining variables. BIGINT - The same as integer, but stores more data than a normal integer. DECIMAL or NUMERIC(M,D) - As the name implies, this data type hold decimal numbers where M denotes the length or total number of digits and D denotes the number of digits after the decimal point. There are a few more data types of this category. Depending on the relational database system, they may or may not have the same names. String data typesCHAR(M) - Fixed length string with the maximum of 255 characters, denoted by the letter M. VARCHAR(M) - Variable length string. The difference between varchar and char is with the way storage is allocated. With char the space is fixed, in other words if you defined the variable to have 20 characters, the system allocates space for 20 characters regardless of whether the value in the field is less than 20 characters long. With varchar, although the value is defined to be 20, if the string is only 10 characters long, the system is only going to allocate 10 character space to that value. Thus cutting down on allocating unused space to variables. BLOB or TEXT - This represents a fields with up to 65535 characters, and is usually used for large amounts of data such as images or other types of files. Date and time data typesDATE - Represents a date value in the format YYYY-MM-DD and the values range between 1000-01-01 to 9999-12-31. DATETIME - Features a date and time combination. For example December 12th 2009 would be recorded as 2009-12-12 00:00:00 this includes time in the format hh:mm:ss in addition to the date, where hh denotes hour, mm denotes minutes and ss denotes seconds. In the next few postings I will explain using a step-by-step approach on how to create a database and tables. From there we will move on to data entry techniques. |
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