Ruby DBI Read Operation
DBI provides a number of different ways to get records from the database. Supposedbh is a database handle,sth is a statement handle:
序号 | 方法 & 描述 |
---|---|
1 | db.select_one( stmt, *bindvars ) => aRow | nil 执行带有bindvars绑定在参数标记前的stmt语句。返回第一行,如果结果集为空则返回nil。 |
2 | db.select_all( stmt, *bindvars ) => [aRow, ...] | nil db.select_all( stmt, *bindvars ){ |aRow| aBlock } 执行带有bindvars绑定在参数标记前的stmt语句。调用不带有块的该方法,返回一个包含所有行的数组。如果给出了一个块,则会为每行调用该方法。 |
3 | sth.fetch => aRow | nil 返回下一行 。如果在结果中没有下一行,则返回nil。 |
4 | sth.fetch { |aRow| aBlock } 为结果集中剩余的行调用给定的块。 |
5 | sth.fetch_all => [aRow, ...] 返回保存在数组中的结果集的所有剩余的行。 |
6 | sth.fetch_many( count ) => [aRow, ...] 返回保存在 [aRow, ...] 数组中的往下第count行。 |
7 | sth.fetch_scroll( direction, offset=1 ) => aRow | nil 返回direction参数和offset指定的行。除了 SQL_FETCH_ABSOLUTE 和 SQL_FETCH_RELATIVE,其他方法都会丢弃参数offset。direction参数可能的值,请查看下面的表格。 |
8 | sth.column_names => anArray 返回列的名称。 |
9 | column_info => [ aColumnInfo, ... ] 返回 DBI::ColumnInfo 对象的数组。每个对象存储有关某个列的信息,并包含该列的名称、类型、精度等其他更多的信息。 |
10 | sth.rows => rpc 返回执行语句处理的行数Count,如果不存在则返回nil。 |
11 | sth.fetchable? => true | false 如果可能获取行,则返回true,否则返回false。 |
12 | sth.cancel 释放结果集所占有的资源。在调用该方法后,您就不能在获取行了,除非再次调用execute。 |
13 | sth.finish 释放准备语句所占有的资源。在调用该方法后,您就不能在该对象上调用其他进一步操作的方法了。 |
direction parameter
The following values can be used direction parameterfetch_scrollmethod:
常量 | 描述 |
---|---|
DBI::SQL_FETCH_FIRST | 获取第一行。 |
DBI::SQL_FETCH_LAST | 获取最后一行。 |
DBI::SQL_FETCH_NEXT | 获取下一行。 |
DBI::SQL_FETCH_PRIOR | 获取上一行。 |
DBI::SQL_FETCH_ABSOLUTE | 获取在该位置偏移处的行。 |
DBI::SQL_FETCH_RELATIVE | 获取距离当前行该偏移量的行。 |
Examples
The following example shows how to get a statement of metadata. Suppose we have the EMPLOYEE table.
#! / Usr / bin / ruby -w require "dbi" begin # Connect to the MySQL server dbh = DBI.connect ( "DBI: Mysql: TESTDB: localhost", "Testuser", "test123") sth = dbh.prepare ( "SELECT * FROM EMPLOYEE WHERE INCOME>? ") sth.execute (1000) if sth.column_names.size == 0 then puts "Statement has no result set" printf "Number of rows affected:% d \ n", sth.rows else puts "Statement has a result set" rows = sth.fetch_all printf "Number of rows:% d \ n", rows.size printf "Number of columns:% d \ n", sth.column_names.size sth.column_info.each_with_index do | info, i | printf "--- Column% d (% s) --- \ n", i, info [ "name"] printf "sql_type:% s \ n", info [ "sql_type"] printf "type_name:% s \ n", info [ "type_name"] printf "precision:% s \ n", info [ "precision"] printf "scale:% s \ n", info [ "scale"] printf "nullable:% s \ n", info [ "nullable"] printf "indexed:% s \ n", info [ "indexed"] printf "primary:% s \ n", info [ "primary"] printf "unique:% s \ n", info [ "unique"] printf "mysql_type:% s \ n", info [ "mysql_type"] printf "mysql_type_name:% s \ n", info [ "mysql_type_name"] printf "mysql_length:% s \ n", info [ "mysql_length"] printf "mysql_max_length:% s \ n", info [ "mysql_max_length"] printf "mysql_flags:% s \ n", info [ "mysql_flags"] end end sth.finish rescue DBI :: DatabaseError => e puts "An error occurred" puts "Error code: # {e.err}" puts "Error message: # {e.errstr}" ensure Connection dbh.disconnect if dbh # disconnect from the server end
This produces the following results:
Statement has a result set Number of rows: 5 Number of columns: 5 --- Column 0 (FIRST_NAME) --- sql_type: 12 type_name: VARCHAR precision: 20 scale: 0 nullable: true indexed: false primary: false unique: false mysql_type: 254 mysql_type_name: VARCHAR mysql_length: 20 mysql_max_length: 4 mysql_flags: 0 --- Column 1 (LAST_NAME) --- sql_type: 12 type_name: VARCHAR precision: 20 scale: 0 nullable: true indexed: false primary: false unique: false mysql_type: 254 mysql_type_name: VARCHAR mysql_length: 20 mysql_max_length: 5 mysql_flags: 0 --- Column 2 (AGE) --- sql_type: 4 type_name: INTEGER precision: 11 scale: 0 nullable: true indexed: false primary: false unique: false mysql_type: 3 mysql_type_name: INT mysql_length: 11 mysql_max_length: 2 mysql_flags: 32768 --- Column 3 (SEX) --- sql_type: 12 type_name: VARCHAR precision: 1 scale: 0 nullable: true indexed: false primary: false unique: false mysql_type: 254 mysql_type_name: VARCHAR mysql_length: 1 mysql_max_length: 1 mysql_flags: 0 --- Column 4 (INCOME) --- sql_type: 6 type_name: FLOAT precision: 12 scale: 31 nullable: true indexed: false primary: false unique: false mysql_type: 4 mysql_type_name: FLOAT mysql_length: 12 mysql_max_length: 4 mysql_flags: 32768