DMX Queries are formulated using the `SELECT` statement. They can extract information from existing data mining models in various ways.
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The purpose of DQL commands is to get the schema relation based on the query passed to it. Although often considered part of DML, the SQL SELECT statement is strictly speaking an example of DQL. When adding FROM or WHERE data manipulators to the SELECT statement the statement is then considered part of the DML.
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A `GROUP BY` statement in SQL specifies that a SQL `SELECT` statement returns a list that is grouped by one or more columns, usually in order to apply some sort of aggregate function to certain columns.
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Despite the difference in syntax, probably one of the closest relative of TNSDL is Go language. Both languages has light-weight processes in their focus. Go's channel are similar to TNSDL INPUTs and Go's select statement on channels allows very similar program design. There are differences, though.
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The default isolation level of different DBMS's varies quite widely. Most databases that feature transactions allow the user to set any isolation level. Some DBMS's also require additional syntax when performing a SELECT statement to acquire locks (e.g. SELECT ... FOR UPDATE to acquire exclusive write locks on accessed rows).
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CUBRID optimizes the common scenario in web applications where database fields need to be incremented on certain events (e.g. page views). In contrast to the usual approach of using a SELECT/UPDATE statement combination, CUBRID can increment fields from within the SELECT statement execution, bypassing some expensive compiling, execution and locking overhead associated with an UPDATE statement.
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StreamSQL extends the type system of SQL to support streams in addition to tables. Several new operations are introduced to manipulate streams. Selecting from a stream - A standard `SELECT` statement can be issued against a stream to calculate functions (using the target list) or filter out unwanted tuples (using a `WHERE` clause). The result will be a new stream.
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For example, the select statement: timer t; uint32_t time; ... select { case t when timerafter(time) :> void: // Action to be performed after the delay ... break; } waits for the timer to exceed the value of before reacting to it. The value of is discarded with the syntax , but it can be assigned to a variable with the syntax .
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An SQL select statement and its result. A database is an organized collection of data, generally stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques. The database management system (DBMS) is the software that interacts with end users, applications, and the database itself to capture and analyze the data.
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Each field may have multiple occurrences, giving SQR the equivalent of two-dimensional arrays. SQR has commands that manipulate multiple items within a single array. SQR has four control structures. The first three are if-else- end, while-end, and evaluate. The fourth is the embedded SQL “select” statement, which allows SQR statements to be executed for each row of data in a loop.
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The client waits on the notification transaction in a select statement for the server to initiate it. A corresponding function can be annotated with , which is called by the slave to clear the notification. In the following simple example: interface I { void f(int x); notification slave void isReady(); clears_notification int getValue(); }; interface I i1, i2; par { for (size_t i=0; i<2; ++i) { // server select { i2.f(int x): i1.
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A `HAVING` clause in SQL specifies that an SQL `SELECT` statement should only return rows where aggregate values meet the specified conditions. It was added to the SQL language because the `WHERE` keyword could not be used with aggregate functions. The `HAVING` clause filters the data on the group row but not on the individual row. To view the present condition formed by the `GROUP BY` clause, the `HAVING` clause is used.
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An `ORDER BY` clause in SQL specifies that a SQL `SELECT` statement returns a result set with the rows being sorted by the values of one or more columns. The sort criteria do not have to be included in the result set. The sort criteria can be expressions, including column names, user-defined functions, arithmetic operations, or `CASE` expressions. The expressions are evaluated and the results are used for the sorting, i.e.
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For example, in the parallel statement: interface I { void f(int x); }; interface I i; par { select { // server i.f(int x): printf("Received %d ", x); break; } i.f(42); // client } the client initiates the transaction , with the parameter value 42, from the interface . The server waits on the transaction (as a case in the select statement) and responds when the client initiates it by printing out a message with the received parameter value.
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SQR has four scalar data types. The first three are numeric (variables begin with “#”), character string (variables begin with “$”), and date (variables begin with “$”, same as with character string variables.). Date variables must be declared, to be distinguished from character string variables. Numeric variables may be of more specific types: integer, floating point,...). Database column variables begin with “&”. The values of database columns are set only by a SQL “select” statement; no other command can change their values.
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The XMOS programming language XC provides a primitive type "chan" and two operators "<:" and ":>" for sending and receiving data from a channel. In this example, two hardware threads are started on the XMOS, running the two lines in the "par" block. The first line transmits the number 42 through the channel while the second waits until it is received and sets the value of x. The XC language also allows asynchronous receiving on channels through a select statement.
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FOR RecordIndex IN (SELECT person_code FROM people_table) LOOP DBMS_OUTPUT.PUT_LINE(RecordIndex.person_code); END LOOP; Cursor-for loops automatically open a cursor, read in their data and close the cursor again. As an alternative, the PL/SQL programmer can pre-define the cursor's SELECT- statement in advance to (for example) allow re-use or make the code more understandable (especially useful in the case of long or complex queries). DECLARE CURSOR cursor_person IS SELECT person_code FROM people_table; BEGIN FOR RecordIndex IN cursor_person LOOP DBMS_OUTPUT.PUT_LINE(recordIndex.
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By default, each task maps to one core on a tile. Because the number of cores is limited (eight in current XCore devices), XC provides two ways to map multiple tasks to cores and better exploit the available cores. Server tasks that are composed of a never-ending loop containing a select statement can be marked as combinable with the attribute . This allows the compiler to combine two or more combinable tasks to run on the same core, by merging the cases into a single select.
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Many databases (such as PostgreSQL) only allow one operation to be performed at a time on each connection. If a request for data (a SQL Select statement) is sent to the database and a result set is returned, the connection is open but not available for other operations until the client finishes consuming the result set. Other databases, like SQL Server 2005 (and later), do not impose this limitation. However, databases that provide multiple operations per connection usually incur far more overhead than those that permit only a single operation task at a time.
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The sequence of actions necessary to execute a query is called a query plan. There might be multiple ways to process the same query. For example, for a query that contains a join statement and a select statement, executing join on both the tables and then executing select on the results would give the same result as selecting from each table and then executing the join, but result in different execution plans. In such case, SQL Server chooses the plan that is expected to yield the results in the shortest possible time.
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Guards are re-evaluated whenever a task leaves the protected object, as this is the only time when the evaluation of guards can have changed. Calls to entries can be requeued to other entries with the same signature. A task that is requeued is blocked and added to the queue of the target entry; this means that the protected object is released and allows admission of another task. The select statement in Ada can be used to implement non-blocking entry calls and accepts, non-deterministic selection of entries (also with guards), time-outs and aborts.
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In terms of the relational model of databases, a table can be considered a convenient representation of a relation, but the two are not strictly equivalent. For instance, a SQL table can potentially contain duplicate rows, whereas a true relation cannot contain duplicate rows that we call as tuples. Similarly, representation as a table implies a particular ordering to the rows and columns, whereas a relation is explicitly unordered. However, the database system does not guarantee any ordering of the rows unless an `ORDER BY` clause is specified in the `SELECT` statement that queries the table.
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In the following example: select { case left :> v: out <: v; break; case right :> v: out <: v; break; } the select statement merges data from and channels on to an channel. A select case can be guarded, so that the case is only selected if the guard expression is true at the same time the event is enabled. For example, with a guard: case enable => left :> v: out <: v; break; the left- hand channel of the above example can only input data when the variable is true. The selection of events is arbitrary, but event priority can be enforced with the attribute for selects.
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Therefore, in addition to the "GIRLS" table we have a table "BOYS" also with the columns "FIRST_NAME" and "LAST_NAME". Now we want to query the last names of all the girls that have the same last name as at least one of the boys. The FO query is {(f,l) : ∃h ( G(f, l) ∧ B(h, l) )}, and the corresponding SQL statement is: select FIRST_NAME, LAST_NAME from GIRLS where LAST_NAME IN ( select LAST_NAME from BOYS ); Notice that in order to express the "∧" we introduced the new language element "IN" with a subsequent select statement. This makes the language more expressive for the price of higher difficulty to learn and implement.
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This design choice has a slight "cost" in that code `else if` branch is, effectively, adding an extra nesting level, complicating the job for some compilers (or its implementers), which has to analyse and implement arbitrarily long `else if` chains recursively. If all terms in the sequence of conditionals are testing the value of a single expression (e.g., `if x=0` ... `else if x=1` ... `else if x=2`...), then an alternative is the switch statement, also called case-statement or select- statement. Conversely, in languages that do not have a switch statement, these can be produced by a sequence of `else if` statements.
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The SQL From clause is the source of a rowset to be operated upon in a Data Manipulation Language (DML) statement. From clauses are very common, and will provide the rowset to be exposed through a Select statement, the source of values in an Update statement, and the target rows to be deleted in a Delete statement. `FROM` is an SQL reserved word in the SQL standard. The `FROM` clause is used in conjunction with SQL statements, and takes the following general form: SQL-DML-Statement FROM table_name WHERE predicate The From clause can generally be anything that returns a rowset, a table, view, function, or system-provided information like the Information Schema, which is typically running proprietary commands and returning the information in a table form.
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Continuous SQL queries in a RDSMS conform to the ANSI SQL standards. The most common RDSMS SQL query is performed with the declarative `SELECT` statement. A continuous SQL `SELECT` operates on data across one or more data streams, with optional keywords and clauses that include `FROM` with an optional `JOIN` subclause to specify the rules for joining multiple data streams, the `WHERE` clause and comparison predicate to restrict the records returned by the query, `GROUP BY` to project streams with common values into a smaller set, `HAVING` to filter records resulting from a `GROUP BY`, and `ORDER BY` to sort the results. The following is an example of a continuous data stream aggregation using a `SELECT` query that aggregates a sensor stream from a weather monitoring station.
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Prior work by WG3 and SC32 mirror bodies, particularly in INCITS DM32, has helped to define a new planned Part 16 of the SQL Standard, which allows a read-only graph query to be called inside a SQL SELECT statement, matching a graph pattern using syntax which is very close to Cypher, PGQL and G-CORE, and returning a table of data values as the result. SQL/PGQ also contains DDL to allow SQL tables to be mapped to a graph view schema object with nodes and edges associated to sets of labels and set of data properties.. The GQL project coordinates closely with the SQL/PGQ "project split" of (extension to) ISO 9075 SQL, and the technical working groups in the U.S. (INCITS DM32) and at the international level (SC32/WG3) have several expert contributors who work on both projects. The GQL project proposal mandates close alignment of SQL/PGQ and GQL, indicating that GQL will in general be a superset of SQL/PGQ.
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