MySQL

Syntax

connect(host, port, user, password, db)

Parameters

• host: A string indicating the address of the MySQL server.
• port: An int indicating the port of the MySQL server.
• user: A string indicating the user name of the MySQL server.
• password: A string indicating the password of the MySQL server.
• db: A string indicating the database name.

Details

Create a connection to the MySQL server. Return a handle of MySQL connection, which will be used for operations including load and loadEx.

Example

conn = mysql::connect(`localhost, 3306, `root, `root, `DolphinDB)

Syntax

showTables(connection)

Parameters

• connection: A MySQL connection handle created with connect.

Details

List all table names in a MySQL database specified in connect.

Examples

conn = mysql::connect(`localhost, 3306, `root, `root, `DolphinDB)
mysql::showTables(conn)

// output:
  Tables_in_DolphinDB
  -------------------
  US

Syntax

extractSchema(connection, tableName)

Parameters

• connection: A MySQL connection handle created with connect.
• tableName: A string indicating the name of a table in MySQL server.

Details

Generate the schema of a table.

Examples

conn = mysql::connect(`localhost, 3306, `root, `root, `DolphinDB)
mysql::extractSchema(conn, `US)

// output:
        name    type        DolphinDBType
        PERMNO  INT         int(11)
        date    DATE        date
        SHRCD   INT         int(11)
        TICKER  SYMBOL      varchar(10)
        ...
        PRC     DOUBLE      double

Syntax

load(connection, table_or_query, [schema], [startRow], [rowNum], [allowEmptyTable])

Parameters

• connection: A MySQL connection handle created with connect.
• table_or_query: A string indicating the name of a MySQL server table or a valid MySQL query such as select * from table limit 100.
• schema: A table containing two STRING type columns. The first represents the column names used to create the result table, and the second represents the target data types. schema can contain additional columns as long as the first two meet the requirements. If we need to change the data type of a column that is automatically determined by the system, the schema table needs to be modified and used as a parameter. schema can be created manually or obtained through the extractSchema method.
• startRow: An integer indicating the index of the starting row to read. If unspecified, read from the first row. If 'table_or_query' is a SQL query, then 'startRow' should be unspecified.
• rowNum: An integer indicating the number of rows to read. If unspecified, read to the last row. If 'table_or_query' is a SQL query, then 'rowNum' should be unspecified.
• allowEmptyTable: A Boolean indicating whether to allow importing an empty table from MySQL The default value is false.This parameter is used to manage the loading restrictions on empty tables.

Details

Load a MySQL table or SQL query result into a DolphinDB in-memory table.

For details about supported data types as well as data conversion rules, please refer to the section of Data Types below.

Examples

conn = mysql::connect(`192.168.1.18, 3306, `root, `root, `DolphinDB)
tb = mysql::load(conn, `US,,0,123456)
select count(*) from tb

conn = mysql::connect(`127.0.0.1, 3306, `root, `root, `DolphinDB)
tb = mysql::load(conn, "SELECT PERMNO FROM US LIMIT 123456")
select count(*) from tb

mysql::load(conn, "SELECT now(6)");

Syntax

loadEx(connection, dbHandle, tableName, partitionColumns, table_or_query, [schema], [startRow], [rowNum], [transform], [sortColumns], [keepDuplicates], [sortKeyMappingFunction])

Parameters

• connection: A MySQL connection handle created with connect.
• dbHandle and tableName: If the input data is to be saved into a distributed database, the database handle and table name should be specified.
• partitionColumns: A STRING scalar/vector indicating partitioning column(s).
• table_or_query: A string indicating the name of a MySQL server table or a valid MySQL query such as select * from table limit 100. Note that the column order of the queried MySQL table is consistent with that of the DolphinDB distributed table; otherwise, value errors or type conversion failures may occur.
• schema: A table containing two STRING type columns. The first represents the column names used to create the result table, and the second represents the target data types. schema can contain additional columns as long as the first two meet the requirements. If we need to change the data type of a column that is automatically determined by the system, the schema table needs to be modified and used as a parameter. schema can be created manually or obtained through the extractSchema method.
• startRow: An integer indicating the index of the starting row to read. If unspecified, read from the first row. If 'table_or_query' is a SQL query, then 'startRow' should unspecified.
• rowNum: An integer indicating the number of rows to read. If unspecified, read to the last row. If 'table_or_query' is a SQL query, then 'rowNum' should unspecified.
• transform: Apply certain transformation on a MySQL table or query before importing into DolphinDB database.
• sortColumns: A string scalar or vector used to specify the sorting column of the table. The written data will be sorted according to sortColumns. This is only required when creating a table with the TSDB engine.
• keepDuplicates: Specifies how to handle data with identical values for all sortColumns within each partition. "ALL" is used to retain all data and is the default value. "LAST" retains only the most recent data. "FIRST" retains only the first piece of data. This is only required when creating a table with the TSDB engine.
• sortKeyMappingFunction: A vector composed of unary function objects, with a length consistent with the index columns, that is, the length of sortColumns minus 1. It specifies the mapping functions to be applied to each column in the index columns in order to reduce the number of sort key combinations. This process is called sort key dimensionality reduction. This is only required when creating a table with the TSDB engine.

Details

Load a MySQL table as a distributed table. The result is a table object with loaded metadata.

For details about supported data types as well as data conversion rules, please refer to the Data Types section.

Examples

• Load data as a partitioned table on disk.

  dbPath = "C:/..."
  db = database(dbPath, RANGE, 0 500 1000)
  mysql::loadEx(conn, db,`tb, `PERMNO, `US)
  tb = loadTable(dbPath, `tb)

• Load data as an in-memory partitioned table

  Load the entire table

  db = database("", RANGE, 0 50000 10000)
  tb = mysql::loadEx(conn, db,`tb, `PERMNO, `US)

  Load via SQL statement

  db = database("", RANGE, 0 50000 10000)
  tb = mysql::loadEx(conn, db,`tb, `PERMNO, "SELECT * FROM US LIMIT 100");

• Load data as a DFS partitioned table

  Load the entire table

  db = database("dfs://US", RANGE, 0 50000 10000)
  mysql::loadEx(conn, db,`tb, `PERMNO, `US)
  tb = loadTable("dfs://US", `tb)

  Load via SQL statement

  db = database("dfs://US", RANGE, 0 50000 10000)
  mysql::loadEx(conn, db,`tb, `PERMNO, "SELECT * FROM US LIMIT 1000");
  tb = loadTable("dfs://US", `tb)

  Load and transform data into a DFS partitioned table

  db = database("dfs://US", RANGE, 0 50000 10000)
  def replaceTable(mutable t){
  	return t.replaceColumn!(`svalue,t[`savlue]-1)
  }
  t = mysql::loadEx(conn, db, "",`stockid, 'select  * from US where stockid<=1000000',,,,replaceTable)

  Load via the schema parameter

  // Obtain the schema of the example table using extractSchema and convert the type of a specific column to DOUBLE
  schema = extractSchema(conn, "example")
  update schema set type = "double" where name = "column"
  
  // Create a database and load the example table to the pt table in the dfs://example database
  db = database("dfs://example", RANGE, 0 50000 1000000 1500000 2000000 2500000 3000001)
  mysql::loadEx(conn, db, `pt, `partitionColumn, "example", schema)

Syntax

close(connection)

Parameters

connection: A MySQL connection handle created with connect.

Details

Disconnect and close the MySQL handle.

Example

mysql::close(conn)

• The numeric types in DolphinDB are all signed types. To prevent overflow, all unsigned types are converted to high-order signed types. For example, unsigned CHAR is converted to signed SHORT, unsigned SHORT is converted to signed INT, etc. 64-bit unsigned types are not supported.
• 'unsigned long long' is not supported in DolphinDB, you can specify schema and use DOUBLE or FLOAT if needed.
• The smallest value of each integral type in DolphinDB is NULL value, e.g. -128 for CHAR, -32,768 for SHORT, -2,147,483,648 for INT and -9,223,372,036,854,775,808 for LONG all mean NULL values in each type respectively.

Note:

• IEEE754 floating-point types are all signed numbers.
• Floating-point types float and double can be converted to numeric types (BOOL, CHAR, SHORT, INT, LONG, FLOAT, DOUBLE) in DolphinDB.
• The newdecimal/decimal type can only be converted to DOUBLE.

• All data types above can be converted to temperal data types in DolphinDB (DATE, MONTH, TIME, MINUTE, SECOND, DATETIME, TIMESTAMP, NANOTIME, NANOTIMESTAMP).

• char and varchar types of length less or equal to 10 will be converted to SYMBOL type in DolphinDB. Other string types will be converted to STRING type in DolphinDB.
• string type will be converted to STRING or SYMBOL type in DolphinDB.

• enum type will be converted to SYMBOL type in DolphinDB.

• CPU: i7-7700 3.60GHZ.
• Hard disk: SSD, read speed 460~500MB/s.

• US stocks daily data from 1990 to 2016 with 22 fields and 50,591,907 rows. Total size is 6.5GB.

160.5 seconds.