- #INFORMIX DBSCHEMA FUNCTION HOW TO#
- #INFORMIX DBSCHEMA FUNCTION PLUS#
The foreign key enforces that data from one column (referencing) must exist in another column (referenced).Įach value of the foreign key column should have a corresponding value in the linked table.
Primary Key - it’s the same as unique indexes, plus the condition that the column is mandatory (it doesn’t allow empty values).Ī foreign key is a column or group of columns in a table that acts as a constraint. If a value is inserted and that value already exists in another record, an error will be displayed. Unique - they don’t allow duplicate values. Extra property for a column - similar to the extra property for type, but at the column level.Īs an index of contents in a book, indexes provide a quick way to find the exact data item you want. 
This is used in the Schema creation scripts. Extra property for type - used only by some databases, may specify some extra text for.Identity - by each 'insert' operation, the column value is autogenerated from an.Samples: a boolean may have as default value true, a number can be 0, and a date can be current_date() Default Value - if no value is specified for the column by insert, this value will be.Mandatory Not null - the column should always have a value.To edit a column just double-click it in the layout diagram.
Learn more about how to create or edit columns here.Īs shown in the first image, each column has a symbol that represents proprieties or foreign keys relations. While the decimal refers to the maximum number of decimal digits. The precision refers to the maximum number of characters allowed in the cells of the columns, Each column can contain only one type of data (numeric, letters, etc.).įor some columns, precision and/or decimal is required.
Edit Options - Edit the table options visually, without having to write any line of code.Īs we mentioned before, every table is made up of columns and rows. We will develop more about constraints further on. Edit Constraints - add or edit check constraints in your table. 
Edit basicĭetails, change the definition of the foreign keys by adding or removing columns, and edit the “On Delete” actions.
Edit Foreign Keys - add or edit foreign keys in your table. Edit Primary Keys - add or edit primary keys or unique indexes in a table. You can change the position of the column in the table and change its visibility. Edit Columns - edit, add, and remove certain columns in the table. You can edit tables in DbSchema by double-clicking on the table header. Find out more about how to create tables here. You can create a table in DbSchema by right-clicking on the empty layout and selecting "Create New Table". If a table holds zero rows, then that table is said to be empty.Įach row is uniquely identified by a primary key, which can be one or more sets of column values. Every table has a primary key column that uniquely identifies the data in the table. Column names can’t beĭuplicated in a table. Columns are defined to hold a specific type of data such as numeric, dates, or text. Each table is made up of columns and rows. We can think of the schema as a blueprint of the database.Ī schema can contain only one table with a certain name.Ī database table is a collection of data focused on a specific topic.Ī database can have more tables related through foreign keys. In the Relational Databases, the schema is composed of a grouping of tables. In this chapter, we will cover some of the key aspects related to the schema definition. Databases store data based on the schema definition, so understanding it is a key part of designing databases.
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