unionM,N: The row refers to the union of the rows with id values of M and N. derivedN: The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause. subqueryN: The row refers to the...
Gets a detailed string representation explaining the AST of this type (with all specifiers and nested constructs such as pointers). This is intended to help debug queries and is a very expensive operation; not to be used in production queries. An example output is “const {pointer to {const...
you can usually find a row in one disk seek (because the index is probablycached). For bigger tables, you can estimate that, using B-tree indexes, youneed this many seeks to find a row: log(row_count) / log(index_block_length / 3* 2 / (index_length +data_pointer_length))...
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pointer to a `sync.Mutex`. Both `WithGroup` and `WithAttrs` copy the handler. Both copies point to the same mutex. If the copy and the original used different mutexes and were used concurrently, then their output could be interleaved, or some output could be lost. Code like this: l2 ...
This tutorial describes how to use Explain reports to locate and fix problematic (slow) queries. It uses the DBT-3 database and begins with the following simple query example. SELECT * FROM orders WHERE YEAR(o_orderdate) = 1992 AND MONTH(o_orderdate) = 4 AND o_clerk LIKE '%0223';As...
second table, the third table, and so on. When all tables areprocessed, MySQL outputs the selected columns and backtracks through the tablelist until a table is found for which there are more matching rows. The nextrow is read from this table and the process continues with the next table...
arraySize :throwinvalid_argument("Array size must be greater than 0") ), ptr(newint[ size ] ) {for( size_t i = 0; i < size; ++i ) ptr[ i ] = 0;// set pointer-based array element}// end Array default constructor// copy constructor for class Array;// must receive a referen...
example 2: Char *ptr = Hello; *ptr =h; / / error The first string is opened with an array, and it is a variable that can be changed. The second string is a constant, or literal value. The PTR simply points to its pointer and cannot change the contents of the pointer. See the ...
Let's start with a simple example:data Status = Green | Yellow | RedThis declares a data type Status which has exactly three different instances. For each instance a data constructor is defined that allows to create a new instance of the data type....