In the event that the string is shorter than the specified length of the CHAR column, PostgreSQL will simply pad the rest with spaces. A column defined as CHAR(50) will have a size within the table that assumes 50 characters. The VAR in VARCHAR is short for 'variable'. The important difference is how they're stored. These are some of the most commonly used string types. The string type is a sequence of "bits" for referring to strings of characters, such as text that says "cat", or the content of a novel. Is the data a flag for a true/false condition?Īfter you answer the above questions, you can then start to choose a type for your column.īelow are some examples of data and their associated column type: DataĮNUM that contains a set of values for all months.Do possible values contain binary data?.Are there multiple possible values from a limited set of values?. If the data is numerical, does it contain negative numbers? What is the largest value it is likely to hold?.Is the data numerical (numbers 0-9) or alphanumerical (numbers 0-9, letters a-z and A-Z)?.In order to determine what type of column should be used, start by thinking about the data that will be stored in the column: Otherwise the database engine will need to convert the values to numbers with every query, and that's an expensive overhead. A column that will only contain numerical data is best defined as a numerical type. The schema creator's goal is optimization. RDBMSs require that you specify a type for every column. Information types What Data Type should I use?Īs a schema creator you have a choice in which types of columns you use, and how many. How data is stored in the columns is important, and the right datatype should be selected for the columns of a table. In contrast, a relational database can contain tables with millions of rows. If we were using a text file to store a small amount of data that did not require optimal searching, it would make little sense to worry too much about how we store the individual pieces of data. The SQL commands in types.sql can also be entered manually into the psql console. Then use the following command to restore the library database: psql -d library < types.sql If you want to follow along, then make sure to have the correct data set up for this chapter it can be found here. As a reminder, a new database can be created using the terminal command createdb db_name. The library database from earlier chapters. You will need a database to run the commands in this chapter.
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