Why Cant You Use Select Statement To Get Generated Keys
- Sql Versus Other Languages
- Why Cant You Use Select Statement To Get Generated Keys Free
- Why Cant You Use Select Statement To Get Generated Keys 2017
- Select Where Statement
- Why Can't You Use Select Statement To Get Generated Keys On Computer
Apr 05, 2019 SQL SELECT INTO – Insert Data from Multiple Tables. In previous examples, we created a table using the SELECT INTO statement from a single table Employee.We can also join multiple tables and use the SELECT INTO statement to create a new table with data as well. 23.1 About Working and Connecting with Databases. The NetBeans IDE allows you to connect to databases and view their content, how to modify database objects, and how to view and change data. It provides drivers for the Java DB, MySQL, Oracle, and PostgreSQL database servers so that you can connect to these databases very easily. The SQL statement “create table as select ” is used to create a normal or temporary table and materialize the result of the select. Some applications use this construct to create a copy of the table. This is one statement that will do all the work, so you do not need to create. Are you working with someone else's schema and they haven't declared nice names for all their constraints? Unfortunately, it is all too easy to create a table like this: Or like this: Sure, you get a little convenience when writing the table. But from now on, you're stuck with weird, system generated. May 09, 2012 This would return you the entries which matched keys from your ITAB specified after FOR ALL ENTRIES. Most of the time, people select the data in ITAB and use that ITAB to get the data from another table. Like, you select the Materials from Sales Order items VBAP and use FOR ALL ENTRIES to select description from MAKT for the selected Materials.
-->A key serves as a unique identifier for each entity instance. Most entities in EF have a single key, which maps to the concept of a primary key in relational databases (for entities without keys, see Keyless entities). Entities can have additional keys beyond the primary key (see Alternate Keys for more information).
By convention, a property named Id or <type name>Id will be configured as the primary key of an entity.
Note
Owned entity types use different rules to define keys.
You can configure a single property to be the primary key of an entity as follows:
You can also configure multiple properties to be the key of an entity - this is known as a composite key. Composite keys can only be configured using the Fluent API; conventions will never setup a composite key, and you can not use Data Annotations to configure one.
Sql Versus Other Languages
Primary key name
By convention, on relational databases primary keys are created with the name PK_<type name>. You can configure the name of the primary key constraint as follows:
Key types and values
While EF Core supports using properties of any primitive type as the primary key, including string, Guid, byte[] and others, not all databases support all types as keys. In some cases the key values can be converted to a supported type automatically, otherwise the conversion should be specified manually.
Why Cant You Use Select Statement To Get Generated Keys Free
Key properties must always have a non-default value when adding a new entity to the context, but some types will be generated by the database. In that case EF will try to generate a temporary value when the entity is added for tracking purposes. After SaveChanges is called the temporary value will be replaced by the value generated by the database.
Important
If a key property has its value generated by the database and a non-default value is specified when an entity is added, then EF will assume that the entity already exists in the database and will try to update it instead of inserting a new one. To avoid this turn off value generation or see how to specify explicit values for generated properties.
Alternate Keys
An alternate key serves as an alternate unique identifier for each entity instance in addition to the primary key; it can be used as the target of a relationship. When using a relational database this maps to the concept of a unique index/constraint on the alternate key column(s) and one or more foreign key constraints that reference the column(s).
Why Cant You Use Select Statement To Get Generated Keys 2017
Tip
If you just want to enforce uniqueness on a column, define a unique index rather than an alternate key (see Indexes). In EF, alternate keys are read-only and provide additional semantics over unique indexes because they can be used as the target of a foreign key.
Select Where Statement
Alternate keys are typically introduced for you when needed and you do not need to manually configure them. By convention, an alternate key is introduced for you when you identify a property which isn't the primary key as the target of a relationship.
You can also configure a single property to be an alternate key:
Why Can't You Use Select Statement To Get Generated Keys On Computer
You can also configure multiple properties to be an alternate key (known as a composite alternate key): Key generator kaspersky pure 3.0.
Finally, by convention, the index and constraint that are introduced for an alternate key will be named AK_<type name>_<property name> (for composite alternate keys <property name> becomes an underscore separated list of property names). You can configure the name of the alternate key's index and unique constraint: