Can a foreign key be NULL and/or duplicate?

Can a foreign key be NULL and/or duplicate?

sql sql-server oracle foreign-keys

sql-server

Is there a combination of "LIKE" and "IN" in SQL?

sql sql-server oracle tsql plsql

sql-server

How do I list all the columns in a table?

sql mysql sql-server database oracle

sql-server

What resources exist for Database performance-tuning? [closed]

mysql sql-server database oracle postgresql

sql-server

update columns values with column of another table based on condition [duplicate]

sql mysql sql-server oracle

sql-server

Oracle: is there a tool to trace queries, like Profiler for sql server? [closed]

sql-server oracle profiler

sql-server

How can I get the number of records affected by a stored procedure?

sql sql-server oracle tsql plsql

sql-server

What is the Oracle equivalent of SQL Server's IsNull() function?

sql-server oracle tsql plsql

sql-server

What is the equivalent of the Oracle "Dual" table in MS SqlServer?

sql-server oracle dual-table

sql-server

Online SQL syntax checker conforming to multiple databases [closed]

mysql sql-server oracle postgresql

sql-server

Relationship between catalog, schema, user, and database instance

mysql sql-server oracle postgresql db2

sql-server

What's the SQL national character (NCHAR) datatype really for?

sql sql-server oracle tsql nvarchar

sql-server

The order of a SQL Select statement without Order By clause

sql-server oracle select sql-order-by

sql-server

How do I decide when to use right joins/left joins or inner joins Or how to determine which table is on which side?

mysql sql sql-server oracle tsql

sql-server

What is the equivalent of varchar(max) in Oracle?

sql sql-server oracle

sql-server