EVOLUTION-MANAGER

Edit File: sql_variant.html

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<table width="100%" summary="page for sql_substr {dbplyr}"><tr><td>sql_substr {dbplyr}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Create an sql translator</h2>

<h3>Description</h3>

<p>When creating a package that maps to a new SQL based src, you'll often
want to provide some additional mappings from common R commands to the
commands that your tbl provides. These three functions make that
easy.
</p>

<h3>Usage</h3>

<pre>
sql_substr(f = "SUBSTR")

sql_str_sub(subset_f = "SUBSTR", length_f = "LENGTH")

sql_paste(default_sep, f = "CONCAT_WS")

sql_paste_infix(default_sep, op, cast)

sql_variant(
  scalar = sql_translator(),
  aggregate = sql_translator(),
  window = sql_translator()
)

sql_translator(..., .funs = list(), .parent = new.env(parent = emptyenv()))

sql_infix(f, pad = TRUE)

sql_prefix(f, n = NULL)

sql_aggregate(f, f_r = f)

sql_aggregate_2(f)

sql_not_supported(f)

sql_cast(type)

sql_log()

sql_cot()

base_scalar

base_agg

base_win

base_no_win

base_odbc_scalar

base_odbc_agg

base_odbc_win
</pre>

<h3>Arguments</h3>

<table summary="R argblock">
<tr valign="top"><td><code>f</code></td>
<td>
<p>the name of the sql function as a string</p>
</td></tr>
<tr valign="top"><td><code>scalar, aggregate, window</code></td>
<td>
<p>The three families of functions than an
SQL variant can supply.</p>
</td></tr>
<tr valign="top"><td><code>..., .funs</code></td>
<td>
<p>named functions, used to add custom converters from standard
R functions to sql functions. Specify individually in <code>...</code>, or
provide a list of <code>.funs</code></p>
</td></tr>
<tr valign="top"><td><code>.parent</code></td>
<td>
<p>the sql variant that this variant should inherit from.
Defaults to <code>base_agg</code> which provides a standard set of
mappings for the most common operators and functions.</p>
</td></tr>
<tr valign="top"><td><code>pad</code></td>
<td>
<p>If <code>TRUE</code>, the default, pad the infix operator with spaces.</p>
</td></tr>
<tr valign="top"><td><code>n</code></td>
<td>
<p>for <code>sql_infix()</code>, an optional number of arguments to expect.
Will signal error if not correct.</p>
</td></tr>
<tr valign="top"><td><code>f_r</code></td>
<td>
<p>the name of the r function being translated as a string</p>
</td></tr>
</table>

<h3>Helper functions</h3>

<p><code>sql_infix()</code> and <code>sql_prefix()</code> create default SQL infix and prefix
functions given the name of the SQL function. They don't perform any input
checking, but do correctly escape their input, and are useful for
quickly providing default wrappers for a new SQL variant.
</p>

<p><code><a href="win_over.html">win_over()</a></code> for helper functions for window functions.
</p>
<p><code><a href="sql.html">sql()</a></code> for an example of a more customised sql
conversion function.
</p>

<h3>Examples</h3>

<pre>
# An example of adding some mappings for the statistical functions that
# postgresql provides: http://bit.ly/K5EdTn

postgres_agg &lt;- sql_translator(.parent = base_agg,
  cor = sql_aggregate_2("CORR"),
  cov = sql_aggregate_2("COVAR_SAMP"),
  sd =  sql_aggregate("STDDEV_SAMP", "sd"),
  var = sql_aggregate("VAR_SAMP", "var")
)

# Next we have to simulate a connection that uses this variant
con &lt;- simulate_dbi("TestCon")
sql_translate_env.TestCon &lt;- function(x) {
  sql_variant(
    base_scalar,
    postgres_agg,
    base_no_win
  )
}

translate_sql(cor(x, y), con = con, window = FALSE)
translate_sql(sd(income / years), con = con, window = FALSE)

# Any functions not explicitly listed in the converter will be translated
# to sql as is, so you don't need to convert all functions.
translate_sql(regr_intercept(y, x), con = con)
</pre>

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