- #Mysql interview questions how to
- #Mysql interview questions full
These compact, unindexed tables are intended for storing and retrieving large amounts of seldom-referenced historical, archived, or security audit information. Because CSV tables are not indexed, you typically keep the data in InnoDB tables during normal operation, and only use CSV tables during the import or export stage. CSV tables let you import or dump data in CSV format, to exchange data with scripts and applications that read and write that same format. Its tables are really text files with comma-separated values. General-purpose and durable way to keep most or all data in memory, and NDBCLUSTER provides fast key-value lookups for huge distributed data sets. Its use cases are decreasing InnoDB with its buffer pool memory area provides a Stores all data in RAM, for fast access in environments that require quick lookups of non-critical data. Table-level locking limits the performance in read/write workloads, so it is often used in read-only or read-mostly workloads in Web and data warehousing configurations. To maintain data integrity, InnoDB also supports FOREIGN KEY referential-integrity constraints. InnoDB stores user data in clustered indexes to reduce I/O for common queries based on primary keys. (without escalation to coarser granularity locks) and Oracle-style consistent nonlocking reads increase multi-userĬoncurrency and performance. That has commit, rollback, and crash-recovery capabilities to protect user data. InnoDB is a transaction-safe (ACID compliant) storage engine for MySQL
Queries that compare variables whose values are not known when the query is compiled and optimized. Queries that involve joining columns through arithmetic or string concatenation operators. Queries that use any of the SQL Server built-in functions or a scalar-valued, user-defined function whose argument is not a constant value. The predicate uses the not equal to (!=) comparison operator or the NOT logical operator. This situation can be especially true if the operator is anything other than the equality (=) operator. The distribution of values in the statistics is not uniform, but the query seeks a highly selective value set. There are no statistics on the columns involved on either side of the operators. Queries with predicates that use operators, and any one of the following are true:. Queries with predicates that use comparison operators between different columns of the same table. Excess usage of cursors and temporary tables. Poorly written query with unnecessarily complicated joins. Procedures and triggers without SET NOCOUNT ON. Excess recompilations of stored procedures. What are the reasons of poor performance of query?įollowing are the reasons for the poor performance of a query: Sixth normal form (6NF): “Table features no non-trivial join dependencies at all”. Domain/key normal form (DKNF): “Every constraint on the table is a logical consequence of the table's domain constraints and key constraints”. Fifth normal form (5NF): “Every non-trivial join dependency in the table is implied by the superkeys of the table”. Fourth normal form: “Every non-trivial multivalued dependency in the table is a dependent on a superkey”. Boyce codd normal form: “every non-trivial functional dependency in the table is dependent on superkey”. Elementary key normal form: superkey dependency or elementary key dependency effects the functional dependency in a table. Third normal form: in a table every non- prime attribute is non-transitively dependent on every candidate key. 
Second normal form: non- prime attributes are not functional dependent on subset of any candidate key. First normal form: in this table represents a relation that has no repeating groups. There are 9 normalizations that are used inside the database. What are the different types of normalization that exists in the database? Select columns c1 and c2 from a table named t1 and joint it to itself using an INNER JOIN clause SELECT c1, c2 FROM t1 A INNER JOIN t2 B on condition Select columns c1 and c2 from a table named t1 and produce a Cartesian product of rows in tables #Mysql interview questions full
Select columns c1 and c2 from a table named t1 and perform a full outer join between t1 and t2 SELECT c1, c2 FROM t1 FULL OUTER JOIN t2 on condition Select columns c1 and c2 from a table named t1 and perform a right join between t1 and t2 SELECT c1, c2 FROM t1 RIGHT JOIN t2 on condition Select columns c1 and c2 from a table named t1 and perform a left join between t1 and t2 SELECT c1, c2 FROM t1 LEFT JOIN t2 on condition Select columns c1 and c2 from a table named t1 and perform an inner join between t1 and t2 SELECT c1, c2 FROM t1 INNER JOIN t2 on condition
#Mysql interview questions how to
How to query data from multiple tables? Sl.No
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