Question

Statement st1 = conn.createStatement();
ResultSet rs2 = st1.executeQuery("
   SELECT cui_2 
   FROM diagnostico.disease_has_symptom, diagnostico.symptom
   WHERE(
      `symptom`.`cui` = `disease_has_symptom`.`cui_2` AND 
      `symptom`.`cui` = " + sintomas.pop() + ");
");

我不知道为什么我会收到这个错误消息...

Answer 1

正如@Brad所示，您的主要问题涉及`symptom`.`cui` = " + sintomas.pop() + ");应该是`symptom`.`cui` = ' + sintomas.pop() + ');的引号混淆：

为什么会这样？根据{{3}}（大多数RDBMS所遵循的SQL语言的正式行业标准的旧版本，包括SQL Server，Oracle，Postgres，MySQL等），单引号和双引号用于不同的目的。

双引号用于标识符，包括列名和表名，例如"symptom"."cui"。

在第5.2节和SQL-ANSI 92 doc下，下面是分隔标识符的函数定义：

<delimited identifier> ::=
   <double quote> <delimited identifier body> <double quote>

以下是此类型的一些常见用法：

根据5.2 - 语法规则

，双引号允许空格

2) With the exception of the <space> character explicitly contained
    in <timestamp string> and <interval string> and the permitted
    <separator>s in <bit string literal>s and <hex string literal>s,
    a <token>, other than a <character string literal>, a <national
    character string literal>, or a <delimited identifier>, shall not 
    include a <space> character or other <separator>.

与常规标识符相比，双引号强加区分大小写：

13)A <regular identifier> and a <delimited identifier> are equivalent 
    if the <identifier body> of the <regular identifier> (with
    every letter that is a lower-case letter replaced by the equiva-
    lent upper-case letter or letters) and the <delimited identifier
    body> of the <delimited identifier> (with all occurrences of
    <quote> replaced by <quote symbol> and all occurrences of <dou-
    blequote symbol> replaced by <double quote>), considered as
    the repetition of a <character string literal> that specifies a
    <character set specification> of SQL_TEXT and an implementation-
    defined collation that is sensitive to case, compare equally
    according to the comparison rules in Subclause 8.2, "<comparison
    predicate>".

但是，某些RDBMS有自己的特殊字符，空格和SQL-92的转义符号，这些符号不是ANSI标准。例如，SQL Server可以使用方括号[...];和MySQL可以使用反引号`...`。

单引号用于将字符串文字括在char，varchar，文本数据类型列（如'C3714552'）中。您引发了错误消息，因为您使用双引号，然后MySQL引擎正在查找列标识符，因为您将值换成双引号。

在reserved words doc的5.3下，下面是字符串文字的定义（不存在双引号）：

 <character string literal> ::=
      [ <introducer><character set specification> ]
      <quote> [ <character representation>... ] <quote>
        [ { <separator>... <quote> [ <character representation>... ] <quote> }... ]

在5.3下 - 语法规则：

 1) In a <character string literal> or <national character string
    literal>, the sequence:

      <quote> <character representation>... <quote>
      <separator>... <quote> <character representation>... <quote>

    is equivalent to the sequence

      <quote> <character representation>... <character representa-
      tion>... <quote>

话虽如此，MySQL提供了各种非ANSI SQL-92，它们可能会使用双引号来表示字符串文字。但可能是后端API，如JDBC或ODBC，驱动程序默认为ANSI标准。

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException：未知列＆＃39; C3714552＆＃39;在＆＃39; where子句＆＃39;

1 个答案: