title: postgreSQL alter column data type to timestamp without time zone
body: <p>I want to alter one column of data from text into type timestamp. There is no time zone in my data. The format of my data is like 28-03-17 17:22, including time and date but no time zone. In other words, all my data are in the same time zone. How can I do it? </p>
  
  <p>I tried multiple ways below, but I still can not find the right approach. Hope you can help me.</p>
  
  <p>Certainly, I can build a new table if my trouble can be solved.</p>
  
  <pre><code>alter table AB
  alter create_time type TIMESTAMP;
  
  ERROR:  column "create_time" cannot be cast automatically to type timestamp without time zone
  HINT:  You might need to specify "USING create_time::timestamp without time zone".
  ********** Error **********
  
  ERROR: column "create_time" cannot be cast automatically to type timestamp without time zone
  SQL state: 42804
  Hint: You might need to specify "USING create_time::timestamp without time zone".
  </code></pre>
  
  
  
  <pre><code>alter table AB
  alter create_time type TIMESTAMP without time zone;
  
  ERROR:  column "create_time" cannot be cast automatically to type timestamp without time zone
  HINT:  You might need to specify "USING create_time::timestamp without time zone".
  ********** Error **********
  
  ERROR: column "create_time" cannot be cast automatically to type timestamp without time zone
  SQL state: 42804
  Hint: You might need to specify "USING create_time::timestamp without time zone".
  </code></pre>
  
  
  
  <pre><code>alter table AB
  alter create_time::without time zone type TIMESTAMP;
  
  ERROR:  syntax error at or near "::"
  LINE 2:  alter create_time::without time zone type TIMESTAM
                            ^
  ********** Error **********
  
  ERROR: syntax error at or near "::"
  SQL state: 42601
  Character: 50
  </code></pre>
  
  
  
  <pre><code>alter table AB
  alter create_time UTC type TIMESTAMP;
  
  ERROR:  syntax error at or near "UTC"
  LINE 2: alter create_time UTC type TIMESTAMP;
                            ^
  ********** Error **********
  
  ERROR: syntax error at or near "UTC"
  SQL state: 42601
  Character: 50
  </code></pre>