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How do you select all columns of all rows from a table?
You select all columns of all rows from a table with the select * from table_name sql statement. Be careful, this can potentially be a very expensive, poor performance, network intensive type of operation - it is better to select only the columns and rows needed.
What condition must be met in SQL when modifying data columns through a view?
1. For Insert - All not null columns of a table must be in view.2. Mostly View uses Joins, make sure all all affected Columns belongs to single table only. (Transaction is possible only on one table per user at any time).3. If view uses any Calculated columns or constant Column then updation is not allowed.4. If view is created using with check option then view can update only those rows which it can show later while running the view.
What is the difference between primary key and unique index?
Primary key is a type of unique index with no null constraint on the columns involved. There can only be one Primary key whereas you can create other unique indexes on the table.
What does projection mean in Oracle?
Projection in Oracle is simply the fields (or columns) you wish to use when building a SELECT query. It is a subset of columns in a table. A projection is nothing but a named list of columns, which you can make use of in your application. Projections have no impact on business rules, they are purely for the use of the user interface. For example: SELECT title, author FROM books; In this case, "title" and "author" would be your projection. Projection means to get data of particular columns in output instead of a whole row or record. In other words, instead of listing values of all the columns for the records if we list values of only particular columns (and not all the columns) then it is known as projection. Foe example: Table Student Roll_No Name Stream Marks 1 ABC Science 590 2. XYZ Commerce 450 Here, query for projection will be: Select Roll_No, Name from Student ; and Output will be: Roll_No Name 1 ABC 2 XYZ or Example: select roll_no where marks>400; ------------------------------------------------------------------------- whereas the selection will be: Select * from Student or Select * from Student where marks > 400 here all the rows and columns of the table will get printed depending on the condition given.
Difference between right join and inner join?
Hi, Natural Join: It is combination or combined result of all the columns in the two tables. It will return all rows of the first table with respect to the second table. Inner Join: This join will work unless if any of the column name shall besxame in two tables
How do you display a subset of columns in SQL?
By putting only the columns that you want to display after the select clause. Example:select colname1, colname2from tablename;
What SQL keyword must be used to remove duplicate rows from the result?
The SQL SELECT DISTINCT StatementIn a table, some of the columns may contain duplicate values. This is not a problem, however, sometimes you will want to list only the different (distinct) values in a table. The DISTINCT keyword can be used to return only distinct (different) values.SQL SELECT DISTINCT SyntaxSELECT DISTINCT column_name(s) FROM table_name
What is the total number of rows and columns required in a table?
How ever many you need to display your data. Only you can determine how many rows and columns you will require in a table you design.
Explain selection union projection operation in DBMS?
Selection: Filters rows in a table based on a specified condition, creating a subset of rows that meet the criteria. Union: Combines the results of two or more SELECT statements into a single result set, removing duplicates. Projection: Selects specific columns from a table or result set, returning only the desired columns and discarding the rest.
What are some of the functions for the alter table command in Oracle?
Some of the functions for the alter table command in Oracle include renaming columns or rows, adding columns or rows and marking items as being read only.
Which columns of the periodic table contains no metallic elements?
The nonmetals are found in columns 14, 15, and 16 of the periodic table. These columns contain elements such as carbon, nitrogen, oxygen, and fluorine, which have properties different from metals, such as being poor conductors of heat and electricity.
How to output only MySQL rows with a certain value?
There are several methods for limiting the output of a query; joins, and a WHERE clause as an example. As an example lets say we have a Customer Table with the following rows CustomerID, FirstName, LastName, Address1, Address2, City, State, PostalCode Now that we have a table lets assume we want to retrieve all records from the table where the Customers LastName = WILLIAMS and they live in the State of OHIO (USA). This query would look like the following: SELECT CustomerID, FirstName, LastName, Address1, Address2, City, State, PostalCode FROM Customers WHERE LastName = 'Williams' AND State = 'OH' If you do not want all of the columns in the table then you would simply modify the SELECT clause to include only those columns that you wish to retrieve. In this example you will want an index on the table that includes the LastName and State fields.
